If you are preparing for GATE 2026 Chemical Engineering, practicing the right type of questions is the key to improving accuracy and score. In the actual exam, GATE almost always tests basic fundamental concepts through MCQs and NAT-type numerical problems, rather than lengthy theory.

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To help students strengthen their basics, we are sharing a few fundamental practice questions in this post. Try to solve them without referring to formulas — this will help boost concept clarity, calculation speed, and exam confidence.

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Practice daily. Analyse your mistakes. Strengthen your fundamentals.
That’s how toppers crack GATE Chemical Engineering with 60–70+ marks.

1. Engineering Mathematics (10 MCQs)

1. A system of linear equations arises from discretizing a PDE and leads to matrix A. If A is symmetric positive definite, which iterative method guarantees convergence for any initial guess?
   a) Jacobi method
   b) Gauss-Seidel method
   c) Conjugate Gradient method
   d) Richardson iteration
   Correct Answer – (c)
   Explanation: Conjugate Gradient converges for symmetric positive definite matrices and is optimal in the associated Krylov subspace.
2. A function f(x,y) has continuous partials. At (1,2) the directional derivative along unit vector u equals 0. Which must be true?
   a) u is orthogonal to gradient f at (1,2)
   b) u is tangent to level curve of f at (1,2) only if gradient is zero
   c) gradient f is zero at (1,2)
   d) u aligns with gradient f at (1,2)
   Correct Answer – (a)
   Explanation: Directional derivative = grad f · u; zero implies u is orthogonal to grad f (unless grad f = 0).
3. The Laplace transform of a causal signal x(t) is X(s). A stable LTI system with transfer function H(s)=1/(s+2) is driven by x(t). Poles of output are at:
   a) s = −2 and poles of X(s)
   b) poles of X(s) shifted by −2
   c) only at poles of X(s)
   d) at s = −2 only
   Correct Answer – (a)
   Explanation: Output Laplace = H(s)X(s); poles are union of poles of H(s) (s = −2) and poles of X(s).
4. For Fourier series of an odd periodic function with period 2π, which coefficients are zero?
   a) All a_n (cosine) coefficients
   b) All b_n (sine) coefficients
   c) Only a_0 is nonzero
   d) Both a_n and b_n are nonzero in general
   Correct Answer – (a)
   Explanation: Odd functions have zero cosine terms (even components vanish), so all a_n including a_0 are zero.
5. Solve approximately using Newton–Raphson a nonlinear root near x0; the method fails to converge when f′(x) is:
   a) zero at root only
   b) zero at iterate
   c) continuous everywhere
   d) sign-changing only at root
   Correct Answer – (b)
   Explanation: Newton needs nonzero derivative at iterate; if f′(x) = 0 at iteration, update becomes ill-conditioned and may fail.
6. For the system x’ = Ax with A having complex conjugate eigenvalues with positive real parts, the origin is:
   a) stable node
   b) asymptotically stable focus
   c) unstable spiral (focus)
   d) center
   Correct Answer – (c)
   Explanation: Complex conjugate eigenvalues with positive real parts give an unstable spiral (solutions spiral outward).
7. The trapezoidal rule for numerical integration is exact for polynomial integrands up to degree:
   a) 0
   b) 1
   c) 2
   d) 3
   Correct Answer – (b)
   Explanation: Trapezoidal rule integrates linear functions exactly (degree ≤1).
8. For the discrete-time convolution y[n]=x[n]*h[n], if x is length M and h is length N, then number of nonzero samples in y is:
   a) M+N
   b) M+N−1
   c) max(M,N)
   d) MN
   Correct Answer – (b)
   Explanation: Linear convolution of finite-length sequences yields length M+N−1.
9. A symmetric matrix has eigenvectors that are:
   a) orthogonal if eigenvalues are distinct
   b) always orthogonal irrespective of eigenvalues
   c) orthogonal only if matrix is diagonalizable
   d) complex conjugate pairs
   Correct Answer – (b)
   Explanation: Real symmetric matrices are orthogonally diagonalizable; eigenvectors can be chosen orthogonal.
10. A PDE u_t = α u_xx is solved by separation of variables in [0,L] with insulated ends; the eigenfunctions are:
    a) sin(nπx/L) only
    b) cos(nπx/L) only
    c) both sin and cos depending on BCs
    d) exponentials only
    Correct Answer – (c)
    Explanation: Insulated (Neumann) BCs lead to cosine modes; Dirichlet lead to sine; choice depends on boundary conditions.

2. Process Calculations & Thermodynamics (10 MCQs)

11. A binary ideal mixture A–B at 1 atm forms a VLE. If activity coefficients are unity, Raoult’s law predicts vapor composition yA. If vapor pressure of A is twice B at same T, then at liquid mole fraction xA = 0.5, vapor mole fraction yA is approximately:
    a) 0.33
    b) 0.5
    c) 0.67
    d) 0.8
    Correct Answer – (c)
    Explanation: yA = xA·P_A°/(xA·P_A° + xB·P_B°); with P_A°=2P_B°, xA=0.5 gives yA = (0.5×2)/(0.5×2+0.5×1)=1/(1+0.5)=2/3 ≈0.67.
12. In a steady-state single-reactor process with no accumulation, total mass balance and component balance are written. If an inert is present, where does it appear in balances?
    a) Only in total mass balance
    b) Only in component balance for inert
    c) Both total and component balances (as part of total)
    d) Nowhere as it doesn’t react
    Correct Answer – (c)
    Explanation: Inert contributes to total mass and has its own component balance (conserved).
13. For a closed system undergoing a reversible adiabatic process, which quantity remains constant?
    a) Enthalpy
    b) Entropy
    c) Internal energy minus PV work
    d) Entropy only for reversible adiabatic — equals constant
    Correct Answer – (d)
    Explanation: Reversible adiabatic implies isentropic (constant entropy).
14. Fugacity of a pure real gas approaches pressure at low pressures. Fugacity coefficient φ = f/P. For ideal gas limit φ →:
    a) 0
    b) 1
    c) ∞
    d) equal to compressibility factor Z
    Correct Answer – (b)
    Explanation: For ideal gas f = P, so φ = 1 at low pressure (ideal limit).
15. In a flash drum at given T and P, if overall feed quality z (mole fraction of volatile) and vapor fraction V/F are known, which relation must be solved?
    a) Material balance only
    b) Equilibrium relation only
    c) Material + equilibrium relations simultaneously (Rachford-Rice equation)
    d) Energy balance only
    Correct Answer – (c)
    Explanation: Flash requires solving material and phase equilibrium (Rachford-Rice) to find compositions and V/F.
16. A reversible refrigerator operates between 0°C (cold) and 30°C (hot). COP (coefficient of performance) of Carnot refrigeration is:
    a) Tc/(Th − Tc) with temperatures in K
    b) Th/(Th − Tc)
    c) (Tc+Th)/Th
    d) independent of temperatures
    Correct Answer – (a)
    Explanation: COP_carnot = T_c/(T_h − T_c) where temperatures in K.
17. For a mixture, partial molar volume is defined as ∂V/∂n_i at constant T,P and other n_j. If partial molar volumes are constant, total volume is:
    a) Sum of partial molar volumes times mole numbers
    b) Ideal mixture volume only if volumes additive
    c) Product of partial molar volumes
    d) Independent of composition
    Correct Answer – (a)
    Explanation: V = Σ n_i × V̄_i when partial molar volumes are constant.
18. An endothermic reaction is carried out in a CSTR with cooling jacket. Increasing coolant flow rate (better cooling) will:
    a) Increase reactor temperature and conversion for endothermic reaction
    b) Decrease reactor temperature and decrease conversion
    c) Decrease temperature and may decrease conversion if reaction rate increases with T
    d) Decrease temperature and typically decrease conversion for endothermic reaction
    Correct Answer – (d)
    Explanation: Endothermic reaction needs heat; better cooling lowers temperature, reducing rate and conversion.
19. The compressibility factor Z for a gas using van der Waals equation near low density behaves as Z ≈ 1 + B’ρ. The sign of B’ indicates:
    a) Attractive forces dominate if B’ < 0
    b) Repulsive forces dominate if B’ < 0
    c) B’ positive means attraction dominates
    d) No relation to forces
    Correct Answer – (a)
    Explanation: Negative virial coefficient indicates net attractive interactions reducing Z below 1.
20. For a closed system, Clausius inequality states ∮δQ/T ≤ 0. Equality holds for:
    a) Irreversible cycle
    b) Reversible cycle
    c) Adiabatic irreversible cycle
    d) Any isothermal cycle
    Correct Answer – (b)
    Explanation: Clausius inequality equality holds for reversible cycles; otherwise strict inequality.

3. Fluid Mechanics (10 MCQs)

21. In laminar flow through circular pipe, velocity profile is parabolic. Average velocity Uavg relates to centerline velocity Umax as:
    a) Uavg = Umax
    b) Uavg = 0.5 Umax
    c) Uavg = 0.67 Umax
    d) Uavg = 0.25 Umax
    Correct Answer – (b)
    Explanation: For laminar (Poiseuille) flow, Umax = 2·Uavg, so Uavg = 0.5 Umax.
22. For flow past a bluff body, drag coefficient CD depends primarily on:
    a) Reynolds number only
    b) Surface roughness only
    c) Both Reynolds number and shape (strouhal number irrelevant)
    d) Fluid viscosity only
    Correct Answer – (c)
    Explanation: CD influenced by Reynolds number and body shape; surface roughness also affects but main are Re and geometry.
23. In a packed bed, Ergun equation combines viscous and inertial losses. If particle size decreases keeping void fraction constant and superficial velocity fixed, pressure drop:
    a) decreases
    b) increases (due to d_p in denominator)
    c) independent of particle size
    d) zero in limit
    Correct Answer – (b)
    Explanation: Ergun shows ΔP ∝ 1/d_p for viscous term and ∝1/d_p for inertial; smaller particles increase ΔP.
24. For compressible flow through a converging nozzle with upstream subsonic conditions, maximum mass flow per area occurs when Mach number at throat is:
    a) 0.3
    b) 0.5
    c) 1 (choked)
    d) depends on Reynolds number
    Correct Answer – (c)
    Explanation: Choked flow at Mach = 1 gives maximum mass flux for given upstream stagnation conditions.
25. A Venturi meter measures flow rate using differential pressure. For same DP, comparing Venturi and orifice plate, the Venturi:
    a) gives higher permanent pressure loss
    b) gives lower pressure recovery and higher loss
    c) has lower permanent pressure loss and higher discharge coefficient
    d) identical performance
    Correct Answer – (c)
    Explanation: Venturi has smoother profile, higher recovery and lower permanent loss than orifice; higher Cd.
26. For two-dimensional incompressible potential flow, velocity potential φ and stream function ψ satisfy Cauchy–Riemann. Hence streamlines and equipotentials are:
    a) Parallel everywhere
    b) Orthogonal everywhere
    c) Coincident for irrotational flow
    d) Not related
    Correct Answer – (b)
    Explanation: φ and ψ are harmonic conjugates; their contours are orthogonal.
27. A fluidized bed becomes bubbling when gas velocity exceeds minimum fluidization velocity by significant margin. Which parameter decreases with increasing superficial velocity beyond minimum?
    a) Bed expansion
    b) Bubble size initially increases, then coalescence affects gas hold-up
    c) Pressure drop across bed decreases proportionally
    d) Particle segregation disappears
    Correct Answer – (b)
    Explanation: As velocity increases more bubbles form and coalesce—bubble size behavior changes; pressure drop roughly remains near weight of bed.
28. In the boundary layer over a flat plate, laminar to turbulent transition location shifts downstream when:
    a) Free stream turbulence intensity increases
    b) Surface is roughened
    c) Fluid viscosity increases significantly
    d) Reynolds number decreases
    Correct Answer – (d)
    Explanation: Lower Reynolds delays transition (shifts downstream). Increased turbulence/roughness promote earlier transition.
29. For parallel flow between two closely spaced plates (lubrication approximation), pressure gradient in flow direction is balanced by:
    a) Inertia only
    b) Viscous shear (dominant)
    c) Gravity only
    d) Turbulent stresses
    Correct Answer – (b)
    Explanation: Lubrication assumes low Reynolds and dominant viscous shear balancing pressure gradient.
30. Dimensional analysis gives Reynolds number Re = ρUD/μ. For two geometrically similar flows, dynamic similarity requires:
    a) Reynolds numbers equal only
    b) Reynolds and Froude numbers equal depending on dominance of inertial/ gravitational effects
    c) Only Froude equal
    d) No similarity conditions
    Correct Answer – (b)
    Explanation: Which dimensionless numbers must match depends on forces: Re for viscous/inertial; Fr for inertial/gravity; both may be needed.

4. Mechanical Operations (10 MCQs)

31. In size reduction by crushing, Rittinger’s law relates energy to:
    a) New surface area generated (proportional)
    b) Mass of product only
    c) Volume reduction linearly
    d) Square of feed size
    Correct Answer – (a)
    Explanation: Rittinger: energy ∝ new surface area (thus inversely with particle size).
32. For a closed-circuit grinding system with classifier, circulating load is defined as:
    a) Fraction of coarse returned to mill per pass
    b) Fraction of fines sent out of circuit
    c) Total mass flow through classifier only
    d) Unrelated to classifier efficiency
    Correct Answer – (a)
    Explanation: Circulating load = mass of material returned to mill divided by product flow, representing recirculation of coarse.
33. In sedimentation, for hindered settling the settling velocity decreases with increasing solids concentration due to:
    a) Increased effective viscosity and particle interactions
    b) Decrease in gravity
    c) Increase in particle density
    d) Laminar flow only
    Correct Answer – (a)
    Explanation: Hindered settling arises from inter-particle interactions and increased effective viscosity reducing terminal velocity.
34. A cyclone separator’s cut diameter d50 reduces when inlet velocity is increased; secondary effects include:
    a) Increased pressure drop and higher collection efficiency for smaller particles
    b) Decreased pressure drop always
    c) No change in collection efficiency
    d) Complete elimination of fines
    Correct Answer – (a)
    Explanation: Higher inlet velocity increases centrifugal forces, improving capture of smaller particles but increases ΔP.
35. For a liquid–solid filtration with cake forming, constant pressure filtration follows what relation between filtrate volume V and time t for compressible cake?
    a) V proportional to t (linear)
    b) t proportional to V^2 for incompressible, but for compressible cake relation is nonlinear and depends on pressure
    c) t independent of V
    d) V exponential in t
    Correct Answer – (b)
    Explanation: For incompressible cake, t∝V^2; compressible cake modifies permeability with pressure making relation more complex.
36. In centrifugation for dewatering, clarification factor G depends on:
    a) Rotor speed squared and geometry (higher G gives higher settling equivalence)
    b) Feed temperature only
    c) Particle material only
    d) Solids concentration only
    Correct Answer – (a)
    Explanation: G = ω^2r/ g average effect; depends on rotational speed and radius (geometry).
37. A tumbling mixer yields good mixing for cohesive powders when:
    a) Cohesive forces are negligible compared to gravitational/ inertia forces
    b) Cohesion dominates leading to poor mixing
    c) Fines reduce mixing always
    d) All powders mix equally
    Correct Answer – (a)
    Explanation: Tumbling effective when cohesive forces small; high cohesion leads to agglomeration and poor mixing.
38. In filtration using a filter press, cake washing efficiency improves when:
    a) Wash fluid per unit cake volume increases and plug flow displacement is approached
    b) Minimal wash fluid is used always
    c) Cake compressibility increases
    d) Wash at higher velocities reduces efficiency
    Correct Answer – (a)
    Explanation: Increasing wash ratio approaches plug flow displacement improving purity; compressibility complicates.
39. For pneumatic conveying of solids, dilute-phase conveying is characterized by:
    a) High gas velocity and low solids concentration with particles suspended
    b) Low gas velocity and dense phase plug flow
    c) Solids conveyed by gravity only
    d) Always lower pipeline wear than dense phase
    Correct Answer – (a)
    Explanation: Dilute-phase uses high gas velocity to suspend particles; dense-phase uses slug/plug flow.
40. Screening efficiency increases with:
    a) Increasing screen aperture size for a fixed feed distribution
    b) Vibratory motion that reduces blinding and promotes stratification
    c) Only by increasing feed rate
    d) Coarser feed particles always
    Correct Answer – (b)
    Explanation: Vibration reduces blinding, aids stratification and passing, improving efficiency for given apertures.

5. Heat Transfer (10 MCQs)

41. For steady one-dimensional conduction through a plane wall with internal heat generation q̇ and thickness 2L, temperature profile is:
    a) Linear
    b) Quadratic (parabolic)
    c) Exponential
    d) Logarithmic
    Correct Answer – (b)
    Explanation: With uniform internal generation, the governing ODE gives a quadratic temperature distribution.
42. In forced convection over a flat plate, local Nusselt number Nu_x scales with Reynolds and Prandtl as:
    a) Nu_x ∝ Re_x^0.5 Pr^1/3 for laminar boundary layer (approx.)
    b) Nu_x ∝ Re_x Pr always
    c) Nu_x independent of Re_x
    d) Nu_x ∝ Re_x^2
    Correct Answer – (a)
    Explanation: For laminar flow, integral/ similarity solutions give Nu_x ∼ 0.332 Re_x^0.5 Pr^1/3 (Blasius/Prandtl relation).
43. A fin with tip convective heat transfer — effectiveness η_f depends on fin parameter mL. As mL → 0 (very short fin), η_f tends to:
    a) 0
    b) 1
    c) ∞
    d) mL
    Correct Answer – (b)
    Explanation: Very short fin behaves like no fin; effectiveness →1 (no enhancement beyond base).
44. For boiling heat transfer, onset of nucleate boiling occurs when:
    a) Surface superheat reaches a threshold allowing bubble nucleation at cavities
    b) Bulk temperature equals critical temperature
    c) Pressure is always constant
    d) Heat flux is zero
    Correct Answer – (a)
    Explanation: Nucleate boiling begins when surface superheat activates nucleation sites overcoming surface tension.
45. In a counterflow heat exchanger, maximum temperature difference between streams occurs at:
    a) Inlet of hot stream only
    b) Outlet of cold stream only
    c) At the end where temperature approaches closer depending on capacity rates, but NTU-LMTD analysis needed; counterflow maximizes mean driving force compared to parallel.
    d) Always zero
    Correct Answer – (c)
    Explanation: Counterflow gives higher terminal temperature approach; specifics need capacity rates; answer indicates counterflow benefits.
46. For radiation between two large parallel gray plates, net radiative heat flux per unit area depends on:
    a) Difference of fourth powers of absolute temperatures divided by sum of resistances including emissivities
    b) Linear difference of temperatures only
    c) Emissivity of only one plate
    d) Independent of separation if view factor is unity
    Correct Answer – (a)
    Explanation: Radiative exchange uses Stefan–Boltzmann and surface resistances; net q ∝ (T1^4 − T2^4)/[(1/ε1)+(1/ε2)−1] for parallel infinite plates.
47. In condensers, filmwise condensation on a vertical plate has heat transfer coefficient h ∝ (k^3 ρ^2 g (ρ−ρ_v) / (μ L ΔT))^1/4. Increasing condensate viscosity μ:
    a) increases h
    b) decreases h
    c) no effect
    d) makes condensation instantaneous
    Correct Answer – (b)
    Explanation: h ∝ μ^(−1/4), so increased viscosity reduces heat transfer coefficient.
48. LMTD method fails for which exchanger scenario and NTU method should be used?
    a) When there is phase change in one stream and flow arrangement complex or unknown heat capacity rates or variable properties causing log mean difference invalid
    b) Always valid
    c) Never fails for counterflow
    d) For single-phase only
    Correct Answer – (a)
    Explanation: LMTD assumes constant specific heats and known inlet/outlet temps; NTU-effectiveness is used when outlet temps unknown or varying properties/phase change.
49. For transient conduction in a large Biot number object (Bi ≫ 1), temperature within body:
    a) Uniform (lumped)
    b) Nonuniform, surface resistance negligible relative to internal conduction, so internal gradients matter
    c) Lumped capacitance valid
    d) Independent of time
    Correct Answer – (b)
    Explanation: Large Bi means internal conduction resistance significant; cannot use lumped capacitance; internal gradients important.
50. In a shell-and-tube heat exchanger with baffle spacing decreased, expected effect:
    a) Decrease heat transfer due to lower turbulence
    b) Increase shell-side heat transfer due to higher crossflow velocity but also increase pressure drop
    c) No effect on ΔP
    d) Only affects tube-side heat transfer
    Correct Answer – (b)
    Explanation: Closer baffles increase shell-side velocity and turbulence improving heat transfer but increase pressure drop.

6. Mass Transfer (10 MCQs)

51. In distillation, relative volatility α_AB = (y_A/x_A)/(y_B/x_B). If α ≈ 1, separation by simple distillation is:
    a) Easy
    b) Difficult or impossible (requires many stages or azeotrope handling)
    c) Independent of α
    d) Achieved in single stage
    Correct Answer – (b)
    Explanation: α≈1 indicates similar volatilities, needing many stages or special techniques.
52. For a single ideal stage absorber with countercurrent flow at steady state, which assumption simplifies design?
    a) Equilibrium between phases at stage contacts
    b) Plug flow in both phases always
    c) Negligible mass transfer driving force
    d) Infinite number of stages
    Correct Answer – (a)
    Explanation: Stagewise equilibrium assumption allows using equilibrium relationships to design.
53. In gas absorption with chemical reaction (fast irreversible), the enhancement factor E > 1. For very fast reaction, mass transfer is controlled by:
    a) Gas-phase resistance only
    b) Liquid-phase reaction and diffusion within liquid film (liquid-side control)
    c) Both phases equally
    d) Solid catalyst only
    Correct Answer – (b)
    Explanation: Fast liquid-phase reaction consumes absorbed species rapidly—liquid film diffusion becomes controlling.
54. For molecular diffusion in stagnant binary mixture, Fick’s law gives flux proportional to concentration gradient. If chemical reaction consumes diffusing species, steady concentration profile becomes:
    a) Linear always
    b) Exponential depending on reaction kinetics and diffusion coefficient
    c) Independent of reaction
    d) Oscillatory
    Correct Answer – (b)
    Explanation: Reaction–diffusion equations typically yield exponential-type profiles under first-order consumption.
55. In tray distillation, efficiency decreases relative to ideal when:
    a) Liquid redistributes uniformly
    b) Hydraulic weeping or entrainment occurs causing deviation from equilibrium
    c) Tray spacing increased always improves efficiency
    d) Higher reflux always decreases efficiency
    Correct Answer – (b)
    Explanation: Weeping/entrainment reduce contact and effective mass transfer lowering tray efficiency.
56. For binary liquid–liquid extraction, distribution coefficient K_D = C_solute,org/C_solute,aq. If K_D is large, extraction:
    a) Favours organic phase and fewer stages required
    b) Requires many stages
    c) Impossible to separate
    d) Independent of feed composition
    Correct Answer – (a)
    Explanation: Large K_D means solute prefers organic, making extraction efficient needing fewer stages.
57. Drying of a porous solid shows constant rate period followed by falling rate period. Falling-rate period is controlled by:
    a) External film diffusion only
    b) Internal moisture diffusion within solid matrix
    c) Convective heat transfer only
    d) Vapor-phase condensation
    Correct Answer – (b)
    Explanation: After surface moisture removed, moisture movement from interior to surface (internal diffusion) controls drying.
58. For adsorption equilibrium, Langmuir isotherm assumes:
    a) Monolayer adsorption on finite identical sites with no interactions
    b) Multilayer adsorption unlimited
    c) Homogeneous surface only temperature dependent
    d) Linear isotherm at all concentrations
    Correct Answer – (a)
    Explanation: Langmuir model postulates monolayer coverage on finite sites and no lateral interactions.
59. In distillation column design using McCabe–Thiele, feed condition is represented by q-line. If feed is saturated vapor, slope of q-line is:
    a) Infinite (vertical)
    b) Zero (horizontal)
    c) Unity (45°)
    d) Negative
    Correct Answer – (a)
    Explanation: q = 0 for saturated vapor so q-line vertical in x–y diagram.
60. For packed columns, pressure drop per unit height increases with liquid flow due to:
    a) Increased mobilization of packing and two-phase interactions raising holdup and frictional losses
    b) Liquid flow always decreases ΔP
    c) Only gas flow affects ΔP
    d) Packing eliminates pressure drop
    Correct Answer – (a)
    Explanation: Two-phase flow friction increases with liquid and gas velocities raising pressure drop.

7. Chemical Reaction Engineering (10 MCQs)

61. For isothermal irreversible first-order reaction A → products in PFR, conversion X relates to space time τ and rate constant k by:
    a) τ = (1/k) ln(1/(1−X))
    b) τ = (1/k) X/(1−X)
    c) τ = (1/k) X
    d) τ independent of X
    Correct Answer – (a)
    Explanation: For first-order in PFR, integrated form gives τ = (1/k) ln(1/(1−X)).
62. For second-order reversible reaction 2A ⇌ B, steady-state conversion in an ideal CSTR depends critically on:
    a) Residence time and equilibrium constant; CSTR may have lower conversion than PFR for same τ
    b) Only kinetics, equilibrium irrelevant
    c) Temperature only
    d) Volume only
    Correct Answer – (a)
    Explanation: Reversible reactions have equilibrium constraints and CSTR behavior depends on τ and K_eq; PFR often gives higher conversion for irreversible.
63. Space time τ is defined as reactor volume divided by volumetric feed. For a CSTR treating a first-order decay, to achieve conversion X, τ required scales as:
    a) τ = X/(k(1−X))
    b) τ = (1/k) ln(1/(1−X))
    c) τ = X/k
    d) τ independent of X
    Correct Answer – (a)
    Explanation: For first-order in CSTR, mass balance gives X = kτ/(1 + kτ) → τ = X/(k(1−X)).
64. Residence Time Distribution (RTD) of an ideal CSTR follows:
    a) E(t) = (1/τ) exp(−t/τ) for t ≥ 0
    b) Dirac delta at τ
    c) Uniform distribution between 0 and 2τ
    d) Gaussian centered at τ
    Correct Answer – (a)
    Explanation: CSTR RTD is exponential with mean τ.
65. For heterogeneous catalytic reactions in packed-bed reactor, effectiveness factor η accounts for:
    a) Internal diffusion limitations reducing observed rate relative to surface rate
    b) Only external mass transfer resistance
    c) Catalyst shape irrelevant
    d) Reaction order must be zero
    Correct Answer – (a)
    Explanation: η < 1 when internal pore diffusion limits reaction rate compared to intrinsic surface kinetics.
66. In autocatalytic reactions, the reaction rate can accelerate as product forms; such kinetics often yield:
    a) Induction period followed by rapid conversion and possible multiple steady states in CSTR
    b) Simple first-order behavior always
    c) No dependence on initial concentration
    d) Monotonic deceleration only
    Correct Answer – (a)
    Explanation: Autocatalysis can show induction then runaway and multiple steady states due to nonlinear kinetics.
67. For non-isothermal reactor design, thermal runaway is likely when:
    a) Heat generated by reaction increases faster with temperature than heat removed by cooling (Arrhenius effect)
    b) Heat removal increases faster than heat generation always
    c) Activation energy is zero
    d) Reaction is endothermic only
    Correct Answer – (a)
    Explanation: Runaway arises when d(heat generation)/dT > d(heat removal)/dT causing positive feedback.
68. For parallel consecutive reactions A → B (k1) and A → C (k2) with k1 ≫ k2, selectivity to B at low conversion is approximately:
    a) k1/(k1+k2) ≈ 1
    b) k2/(k1+k2)
    c) independent of k values
    d) zero
    Correct Answer – (a)
    Explanation: At low conversion, probabilities proportional to rate constants; dominant k1 yields high selectivity to B.
69. A diffusion-controlled reaction in porous catalyst shows Thiele modulus φ ≫ 1. Effectiveness factor approaches:
    a) 1
    b) 0 (∝1/φ)
    c) Infinity
    d) Negative values
    Correct Answer – (b)
    Explanation: For φ≫1, internal diffusion limits, η ~ 1/φ (small); overall rate much less than intrinsic surface rate.
70. For gas-phase reactions where rate ∝ p_A^n, if reaction order n < 1, doubling partial pressure increases rate by less than twofold due to:
    a) Adsorption effects or non-ideal kinetics leading to fractional orders
    b) Ideal gas law only
    c) Catalyst temperature only
    d) No physical basis
    Correct Answer – (a)
    Explanation: Fractional orders often arise from adsorption/ surface coverage phenomena leading to sublinear pressure dependence.

8. Instrumentation & Process Control (10 MCQs)

71. A first-order process with dead time is controlled by a PI controller tuned by Ziegler–Nichols. Increasing proportional gain beyond stability margin causes:
    a) Oscillations and possible instability due to reduced phase margin
    b) Improved stability always
    c) No change in transient response
    d) Integrator windup elimination
    Correct Answer – (a)
    Explanation: High Kp reduces phase margin causing oscillations; Z–N gives aggressive tuning near stability.
72. For a linear time-invariant system, Bode plot magnitude and phase can predict closed-loop stability using:
    a) Nyquist criterion or gain and phase margins derived from Bode
    b) Only time domain step response
    c) Root locus not related
    d) None of above
    Correct Answer – (a)
    Explanation: Bode plots give gain/phase margins used to infer stability; Nyquist is equivalent frequency-domain test.
73. A thermocouple sensor measures temperature based on:
    a) Seebeck effect (thermoelectric voltage proportional to temperature difference)
    b) Resistance change only (that’s RTD)
    c) Capacitance change
    d) Optical emission
    Correct Answer – (a)
    Explanation: Thermocouples generate EMF due to Seebeck effect; RTDs use resistance-temperature relation.
74. For a control loop with significant dead time, which controller strategy improves performance?
    a) Smith predictor to compensate dead time
    b) Simple P-only always best
    c) Removing integrator always helps
    d) Cascading two P controllers
    Correct Answer – (a)
    Explanation: Smith predictor models plant+dead-time structure to mitigate effect of large delays improving control.
75. Process variable measurement with nonlinearity can be linearized using:
    a) Sensor characterization and retransmission with linearizing function (static linearization)
    b) Ignoring nonlinearity always acceptable
    c) Tuning PID only fixes sensor nonlinearity
    d) Changing range only
    Correct Answer – (a)
    Explanation: Static/dynamic linearization maps sensor output to linearized variable via calibration or hardware/software compensation.
76. In feedback control, integral action eliminates steady-state error for step disturbances when:
    a) The loop is type 1 or higher (presence of integrator in loop)
    b) Always regardless of controller tuning
    c) Only derivative action can eliminate steady-state error
    d) Loop gain is zero
    Correct Answer – (a)
    Explanation: Integral action introduces pole at origin in loop transfer function, eliminating steady-state error to step inputs for type ≥1.
77. A PID controller derivative term is sensitive to measurement noise. Practical implementations use:
    a) Filtered derivative (derivative on measurement with a low-pass filter)
    b) Infinite derivative gain
    c) No filtering required
    d) Derivative in parallel with integral yields noise immunity
    Correct Answer – (a)
    Explanation: Derivative amplifies high-frequency noise; filtering derivative term reduces sensitivity.
78. For measuring very low flow rates of gas, which sensor is best for range and low pressure drop?
    a) Thermal mass flow meter (direct mass measurement, low ΔP)
    b) Orifice plate
    c) Venturi only
    d) Rotameter always best
    Correct Answer – (a)
    Explanation: Thermal mass flow meters measure mass flow independent of pressure/ temperature and offer low pressure loss for low flows.
79. A PID controller in series (cascade) with inner fast loop and outer slow loop is advantageous when:
    a) Inner loop controls fast dynamics (e.g., flow), improving outer loop performance (e.g., level)
    b) Always worse than single loop
    c) Only for temperature control always
    d) Not used in process industries
    Correct Answer – (a)
    Explanation: Cascade control isolates fast dynamics improving disturbance rejection and overall stability.
80. Sensor calibration drift results in biased measurements. Best practice to handle drift is:
    a) Periodic calibration against standards and adding diagnostics/auto-zero where feasible
    b) Ignoring small drift always safe
    c) Replace sensor every week irrespective of condition
    d) Increase controller gain to compensate
    Correct Answer – (a)
    Explanation: Calibration ensures accuracy; diagnostics and scheduled recalibration manage drift; controller tuning cannot correct measurement bias.

9. Plant Design & Economics (10 MCQs)

81. In preliminary plant design, the Lang factor multiplies purchased equipment cost to estimate:
    a) Total installed cost including piping, instrument, insulation etc.
    b) Only piping cost
    c) Operating cost per year
    d) Raw material cost
    Correct Answer – (a)
    Explanation: Lang factors are empirical multipliers to convert equipment purchase cost to total installed capital cost.
82. Net Present Value (NPV) of a project is positive when:
    a) Present value of cash inflows exceeds present value of cash outflows at chosen discount rate
    b) Payback period is less than plant life always
    c) Depreciation is zero
    d) Operating cost exceeds revenue
    Correct Answer – (a)
    Explanation: Positive NPV indicates discounted benefits exceed costs, justifying investment.
83. For pump selection in a process plant, key design inputs include:
    a) Required flow rate, total head, fluid properties, allowable NPSH, and efficiency curves
    b) Only power availability
    c) Color of pump
    d) Vendor preference only
    Correct Answer – (a)
    Explanation: Pump sizing requires flow, head, fluid characteristics and NPSH to ensure cavitation-free operation and efficiency.
84. Piping layout in plant design minimizes:
    a) Total pipe length and number of crossings while maintaining accessibility and safety; pressure drop considerations included
    b) Only aesthetic appeal
    c) Always maximum length for flexibility
    d) Independent of equipment layout
    Correct Answer – (a)
    Explanation: Good piping design optimizes length, minimizes pressure drop, ensures maintenance access and safety.
85. For economic comparison of two processes with different lifespans, equivalent annual cost (EAC) method:
    a) Converts NPV into annualized cost allowing comparison at same time base
    b) Uses payback period only
    c) Ignores salvage value
    d) Applies only to identical lifespans
    Correct Answer – (a)
    Explanation: EAC annualizes costs for fair comparison across different project lives.
86. Heat exchanger area estimation uses log mean temperature difference (LMTD). If fouling factors increase, required area:
    a) Increases to compensate thermal resistance
    b) Decreases always
    c) Unchanged
    d) Infinite
    Correct Answer – (a)
    Explanation: Fouling adds thermal resistance reducing overall U; to maintain duty area must increase.
87. In safety design, inherently safer design prefers:
    a) Substitution, minimization, moderation, simplification over add-on protective measures
    b) Adding more relief valves only
    c) Relying solely on administrative controls
    d) Increasing stored hazardous inventory for better control
    Correct Answer – (a)
    Explanation: Inherently safer design reduces hazard at source via substitution/minimization rather than external controls.
88. For scaling up a stirred tank reactor from lab to plant, geometric similarity plus constant tip speed does not guarantee similar mixing because:
    a) Reynolds number and power per unit volume must be considered for mixing time similarity
    b) Only geometry matters
    c) Scale-up trivial always
    d) Mixing scales linearly with volume
    Correct Answer – (a)
    Explanation: Similar mixing requires matching relevant dimensionless numbers (Re, power/volume, mixing time) not just geometry.
89. Depreciation using straight-line method yields annual depreciation equal to:
    a) (Initial cost − salvage value)/useful life
    b) Initial cost divided by salvage value
    c) Salvage value only
    d) Not used for plant economics
    Correct Answer – (a)
    Explanation: Straight-line depreciation allocates cost evenly: (cost − salvage)/life.
90. For economic risk analysis, sensitivity analysis identifies:
    a) Parameters with largest impact on NPV or IRR; helps prioritize areas for uncertainty reduction
    b) Only nominal values matter
    c) Sensitivity increases expected profit automatically
    d) Always eliminates uncertainty
    Correct Answer – (a)
    Explanation: Sensitivity shows how outputs respond to input variations informing risk mitigation.

10. Chemical Technology (10 MCQs)

91. Steam reforming of methane (CH4 + H2O → CO + 3H2) is endothermic and industrially favored at:
    a) High temperatures (700–1000°C) and low pressure to favour H2 per reaction stoichiometry but practical pressures used for downstream shifts/ compression
    b) Low temperature only
    c) High pressure only always best
    d) Room temperature with catalyst
    Correct Answer – (a)
    Explanation: Steam reforming is endothermic requiring high T; pressure trade-offs consider equilibrium and downstream processing.
92. Haber process for ammonia synthesis operates at elevated pressure because:
    a) Reaction reduces number of moles (4 → 2), so high pressure shifts equilibrium to ammonia by Le Chatelier’s principle
    b) High pressure slows the reaction always
    c) Low pressure is preferred to increase yield
    d) Pressure irrelevant
    Correct Answer – (a)
    Explanation: High pressure favors ammonia formation due to mole reduction despite kinetic trade-offs.
93. In contact process for sulfuric acid manufacture, catalyst activity for SO2 → SO3 depends on:
    a) Temperature and catalyst surface area; optimal temperature balances kinetics and equilibrium for conversion
    b) Only pressure matters
    c) Catalyst never deactivates
    d) Reaction is non-catalytic
    Correct Answer – (a)
    Explanation: Vanadium pentoxide catalysts active over specific T; conversion depends on kinetics, equilibrium and catalyst properties.
94. Fluid catalytic cracking (FCC) in petroleum refining uses a circulating riser-regenerator system primarily to:
    a) Circulate catalyst between reactor and regenerator burning coke to restore activity and maintain catalyst inventory
    b) Separate oil and catalyst permanently
    c) Avoid catalyst circulation entirely
    d) Reduce residence time of vapors only
    Correct Answer – (a)
    Explanation: FCC continually circulates catalyst; coke burnt in regenerator to restore catalyst and heat.
95. In polymerization for polyethylene, Ziegler–Natta catalysts produce polymers with:
    a) Higher stereoregularity and broader molecular weight control compared to free-radical methods
    b) Always amorphous polymer only
    c) No control over molecular weight
    d) Not used industrially
    Correct Answer – (a)
    Explanation: Z–N catalysts allow stereoregular polymerization with control over molecular properties.
96. Claus process converts H2S to elemental sulfur. For efficient operation, the ratio of air to acid gas must be controlled to:
    a) Provide partial combustion to generate SO2 yet maintain overall stoichiometry for Claus reaction without excess SO2 or H2S
    b) Completely oxidize all H2S to SO2 only
    c) Always operate fuel-rich with no oxygen
    d) Not important
    Correct Answer – (a)
    Explanation: Partial oxidation produces SO2 which reacts with remaining H2S to form sulfur; stoichiometric balance is critical.
97. In fertilizer industry, ammonia is commonly used to make ammonium nitrate; safety concern due to oxidizer–fuel mix can be mitigated by:
    a) Proper dilution, temperature control, and avoiding contamination with organics to prevent runaway decomposition
    b) Increasing storage temperature
    c) Adding fuel to neutralize oxidizer
    d) None required if stored indoors
    Correct Answer – (a)
    Explanation: Ammonium nitrate can be explosive under contamination and heating; controls reduce hazard.
98. In large-scale electrochemical processes (e.g., chlor-alkali), cell efficiency depends on:
    a) Current efficiency, membrane selectivity, electrode overpotentials and energy consumption per unit product
    b) Only electrode color
    c) Temperature irrelevant
    d) Only theoretical cell potential matters
    Correct Answer – (a)
    Explanation: Practical efficiency includes losses from overpotentials, side reactions and membrane crossover.
99. In hydrotreating of fuels, hydrogen partial pressure is important because:
    a) It suppresses coke and sulfur formation and shifts hydrogenation reactions favorably improving product quality
    b) High H2 always reduces conversion
    c) Pressure has no effect on sulfur removal
    d) Hydrogen partial pressure only affects color
    Correct Answer – (a)
    Explanation: Higher H2 partial pressure promotes hydrogenation, reducing coke and enabling sulfur removal.
100. For large exothermic polymerization reactors, temperature control via cooling jackets is challenging due to:
     a) Heat removal limitations and possible hot spots; staged addition or loop reactors often used to manage heat
     b) Cooling jackets always sufficient regardless of scale
     c) Heat generation negligible
     d) Reactor volume independent of heat removal needs
     Correct Answer – (a)
     Explanation: High heat fluxes demand advanced cooling and reactor configuration to avoid runaway and ensure product quality.

11. General Aptitude (English + Quantitative) (10 MCQs)

101. (Verbal) Read the short passage: “The committee’s report, while comprehensive, offered few actionable recommendations; stakeholders sought a roadmap rather than descriptive analysis.” The author’s tone is best described as:
     a) Laudatory
     b) Critical but constructive
     c) Indifferent
     d) Sarcastic
     Correct Answer – (b)
     Explanation: Sentence indicates critique (few actionable recommendations) with implied desire for improvement—constructive criticism.
102. (Verbal) Choose the most appropriate single-word substitution: A person skilled at making persuasive speeches is called:
     a) Orator
     b) Scribe
     c) Procurer
     d) Auditor
     Correct Answer – (a)
     Explanation: Orator denotes skilled public speaker.
103. (Quant) A candidate solves a numerical integration using Simpson’s rule with n=4 subintervals and obtains I_simpson. If the fourth derivative of integrand is large, Simpson’s rule error:
     a) May be significant as error ∝ (b−a)^5 f^(4)(ξ)/180 n^4
     b) Is zero always
     c) Independent of f^(4)
     d) Improved with larger h
     Correct Answer – (a)
     Explanation: Simpson error term involves the fourth derivative; large f^(4) increases error for fixed n.
104. (Quant) If two events A and B are independent and P(A)=0.3, P(B)=0.4, then probability exactly one occurs is:
     a) 0.46
     b) 0.12
     c) 0.7
     d) 0.5
     Correct Answer – (a)
     Explanation: P(A xor B) = P(A)+P(B)−2P(A)P(B) = 0.3+0.4−2(0.12)=0.7−0.24=0.46.
105. (Quant) A candidate has to allocate study time between 3 subjects in ratio 2:3:5. If total time is 100 hours, time for second subject is:
     a) 30 hours
     b) 20 hours
     c) 50 hours
     d) 40 hours
     Correct Answer – (d)
     Explanation: Sum ratio =10 parts; second subject =3/10 ×100 =30 (but wait check: ratio 2:3:5 sum=10; second =3/10*100=30). Correction: answer should be 30. Choose accordingly.
     Correct Answer – (a)
     Explanation: 3/10 of 100 = 30 hours.
106. (Quant) A GATE-like numerical: If the standard deviation of a set is σ and you add a constant c to every element, new σ is:
     a) σ (unchanged)
     b) σ + c
     c) σ^2 + c^2
     d) σ*c
     Correct Answer – (a)
     Explanation: Adding constant shifts mean but does not change spread (standard deviation).
107. (Verbal) Choose the option that best completes: “Although the hypothesis seemed plausible, further experiments ______ the initial assumption.”
     a) corroborated
     b) undermined
     c) embellished
     d) clarified
     Correct Answer – (b)
     Explanation: Context indicates experiments contradicted or weakened assumption—undermined fits.
108. (Quant) For sequences a_n defined by a_{n+1} = r a_n with a_0 ≠ 0, the sequence converges to 0 iff:
     a) |r| < 1
     b) r > 1
     c) r = 1
     d) |r| > 1
     Correct Answer – (a)
     Explanation: Geometric sequence decays to zero for |r| < 1.
109. (Quant) A student estimates probability of answering an MCQ correctly by elimination: from 4 options, two clearly wrong, then guessing between remaining two gives probability of correct =
     a) 0.5
     b) 0.25
     c) 0.75
     d) 1.0
     Correct Answer – (a)
     Explanation: After eliminating two, random guess among two gives 1/2.
110. (Verbal) Which sentence is grammatically correct?
     a) He is more clever than anyone in the class.
     b) He is the most clever of all the students.
     c) He is cleverer than all of students.
     d) He is cleverer than anyone else in the class.
     Correct Answer – (d)
     Explanation: “Cleverer than anyone else in the class” is grammatically and idiomatically correct.

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