Adsorption method MCQs With Answer

Adsorption method MCQs With Answer

Adsorption is a key physicochemical process in pharmaceutics that governs drug stability, formulation, purification, and toxicology. This comprehensive set of MCQs for B. Pharm students explores adsorption principles, adsorption isotherms (Langmuir, Freundlich, BET), adsorption kinetics and thermodynamics, adsorbents (activated charcoal, silica gel, ion-exchange resins), surface area and pore-size effects, column and batch adsorption, regeneration and breakthrough curves, and practical pharmaceutical applications such as taste masking, drug purification, and chromatographic separations. Questions emphasize interpretation of isotherm parameters, adsorption capacity units, rate-limiting steps, and real-world formulation implications. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. What is adsorption?

• Accumulation of molecules at the surface of a solid or liquid
• Penetration of molecules into the bulk of a solid
• Formation of a covalent bond with the adsorbent
• Conversion of a gas to a solution

Correct Answer: Accumulation of molecules at the surface of a solid or liquid

Q2. Which thermodynamic nature is most commonly associated with physical adsorption?

• Endothermic process involving bond formation
• Exothermic process due to van der Waals interactions
• Isothermal and entropy-driven
• Always irreversible and highly specific

Correct Answer: Exothermic process due to van der Waals interactions

Q3. Which assumption is central to the Langmuir adsorption isotherm?

• Multilayer adsorption on a heterogeneous surface
• Monolayer adsorption on a homogeneous surface with identical binding sites
• Adsorption capacity increases indefinitely with concentration
• Adsorption energy increases with surface coverage

Correct Answer: Monolayer adsorption on a homogeneous surface with identical binding sites

Q4. The Freundlich isotherm is best described as which of the following?

• A theoretical model assuming uniform adsorption energy
• An empirical model for adsorption on heterogeneous surfaces
• A model that predicts monolayer capacity explicitly
• A model applicable only to gas-phase adsorption

Correct Answer: An empirical model for adsorption on heterogeneous surfaces

Q5. The BET method is primarily used to determine which property of an adsorbent?

• Chemical reactivity with adsorbates
• Specific surface area via multilayer adsorption measurements
• Ion-exchange capacity
• Thermal stability of adsorbent

Correct Answer: Specific surface area via multilayer adsorption measurements

Q6. In pharmacy, activated charcoal is widely used because it has:

• High solubility in gastric fluid
• High surface area and strong non-specific adsorption of toxins
• Selective covalent binding to drugs
• Ion-exchange properties for salts

Correct Answer: High surface area and strong non-specific adsorption of toxins

Q7. Which kinetic model is commonly interpreted as indicating chemisorption?

• Pseudo-first-order (Lagergren) model
• Pseudo-second-order kinetic model
• Zero-order kinetic model
• Freundlich kinetic model

Correct Answer: Pseudo-second-order kinetic model

Q8. Typical units for adsorption capacity in batch studies are given as:

• mol·L
• mg·g⁻¹ (milligrams of adsorbate per gram of adsorbent)
• J·mol⁻¹
• m²·g⁻¹

Correct Answer: mg·g⁻¹ (milligrams of adsorbate per gram of adsorbent)

Q9. A breakthrough curve in a fixed-bed adsorption column plots:

• Adsorbent surface area versus time
• Effluent concentration (C/C0) or concentration versus time or volume of effluent
• Temperature of the bed versus time
• Adsorbent pore size distribution

Correct Answer: Effluent concentration (C/C0) or concentration versus time or volume of effluent

Q10. How does increasing temperature generally affect physical adsorption from a gas or liquid?

• It increases adsorption due to higher diffusion
• It decreases adsorption because physical adsorption is exothermic
• It has no effect on adsorption equilibria
• It always converts physical adsorption into chemisorption

Correct Answer: It decreases adsorption because physical adsorption is exothermic

Q11. Which factor most directly increases adsorption capacity of a porous adsorbent?

• Lower surface area
• Higher surface area and optimal pore volume
• Reduced pore volume
• Decrease in adsorbent particle size without changing surface area

Correct Answer: Higher surface area and optimal pore volume

Q12. For a spontaneous adsorption process at constant temperature and pressure, the sign of Gibbs free energy change (ΔG) is typically:

• Positive
• Zero
• Negative
• Undefined

Correct Answer: Negative

Q13. Which adsorbent is commonly preferred for moisture adsorption in pharmaceutical packaging?

• Activated charcoal
• Silica gel
• Ion-exchange resin
• Polystyrene foam

Correct Answer: Silica gel

Q14. Ion-exchange resins are most suitable for which pharmaceutical application?

• Adsorption of nonpolar organic vapors
• Removal or separation of ionic drugs and counter-ions
• Taste masking of neutral molecules by van der Waals forces
• Thermal reactivation of activated charcoal

Correct Answer: Removal or separation of ionic drugs and counter-ions

Q15. When adsorption exhibits a long tail and slow approach to equilibrium, the likely rate-limiting step is:

• External film diffusion only
• Intraparticle (pore) diffusion within adsorbent particles
• Instantaneous adsorption at the surface
• Chemical reaction producing the adsorbent

Correct Answer: Intraparticle (pore) diffusion within adsorbent particles

Q16. In the Freundlich isotherm, the constant 1/n represents:

• The monolayer adsorption capacity
• Adsorption intensity or surface heterogeneity; values <1 indicate favorable adsorption
• The adsorbent pore size
• The heat of adsorption per mole

Correct Answer: Adsorption intensity or surface heterogeneity; values <1 indicate favorable adsorption

Q17. In the Langmuir equation, the constant b is related to:

• The maximum multilayer capacity
• The equilibrium constant related to affinity between adsorbate and adsorbent
• The surface area exclusively
• The diffusion coefficient in solution

Correct Answer: The equilibrium constant related to affinity between adsorbate and adsorbent

Q18. The preferred industrial method to regenerate spent activated charcoal is:

• Simple rinsing with water
• Thermal reactivation at high temperature in controlled atmosphere
• Freezing to detach adsorbates
• Adding salts to precipitate adsorbates

Correct Answer: Thermal reactivation at high temperature in controlled atmosphere

Q19. Why does solution pH strongly influence adsorption of ionizable drugs?

• Because pH changes the temperature of the solution
• Because pH alters the ionization state of the drug and surface charge of the adsorbent
• Because pH increases adsorbent surface area
• Because pH converts physical adsorption into absorption

Correct Answer: Because pH alters the ionization state of the drug and surface charge of the adsorbent

Q20. An adsorption isotherm plots which variables?

• Amount adsorbed at equilibrium (q_e) versus equilibrium concentration (C_e)
• Temperature versus time
• Adsorbent mass vs particle size
• Pressure versus volume only for liquids

Correct Answer: Amount adsorbed at equilibrium (q_e) versus equilibrium concentration (C_e)

Q21. Which method is commonly used to analyze pore size distribution (mesopores) of an adsorbent?

• Langmuir isotherm analysis
• BJH (Barrett-Joyner-Halenda) method
• Freundlich exponent plot
• Lagergren kinetic plot

Correct Answer: BJH (Barrett-Joyner-Halenda) method

Q22. In the Langmuir model the parameter Qm represents:

• Multilayer adsorption capacity
• Monolayer adsorption capacity at saturation
• Diffusion coefficient of adsorbate
• Surface heterogeneity index

Correct Answer: Monolayer adsorption capacity at saturation

Q23. Which of the following is a characteristic of chemisorption?

• Weak van der Waals interactions only
• Formation of specific chemical bonds and often irreversibility
• Always reversible at room temperature
• Independent of surface chemical nature

Correct Answer: Formation of specific chemical bonds and often irreversibility

Q24. Which linearized form is commonly used to determine Langmuir constants from experimental data?

• Plot of q_e versus C_e directly without transformation
• Plot of 1/q_e versus 1/C_e (reciprocal linear form)
• Plot of log q_e versus log C_e
• Plot of q_e² versus C_e

Correct Answer: Plot of 1/q_e versus 1/C_e (reciprocal linear form)

Q25. Which chromatographic technique primarily depends on adsorption interactions with the stationary phase?

• Size-exclusion chromatography
• Normal-phase (silica) adsorption chromatography
• Ion-exchange chromatography (relies on ionic interactions only)
• Gas chromatography with nonpolar stationary phase only

Correct Answer: Normal-phase (silica) adsorption chromatography

Q26. The Lagergren equation describes which adsorption kinetic order?

• Pseudo-first-order kinetics
• Pseudo-zero-order kinetics
• Pseudo-second-order kinetics
• Michaelis-Menten kinetics

Correct Answer: Pseudo-first-order kinetics

Q27. In competitive adsorption from solution, preferential adsorption of one component is mainly determined by:

• The molecular weight alone
• The relative affinity constants and interaction energies with the adsorbent surface
• The color of the adsorbate
• The viscosity of the solvent only

Correct Answer: The relative affinity constants and interaction energies with the adsorbent surface

Q28. Adsorption typically causes the system entropy (ΔS) to:

• Increase greatly due to ordering at the surface
• Decrease because adsorbate molecules become more ordered on the surface
• Remain unchanged always
• Become positive for all chemisorption processes

Correct Answer: Decrease because adsorbate molecules become more ordered on the surface

Q29. The Langmuir isotherm is most valid under which pressure/concentration conditions for gas adsorption?

• Very high pressures where multilayer formation dominates
• Relatively low pressures/concentrations where monolayer formation is the main process
• Only at the critical point of the gas
• When the adsorbent is chemically reacting with the gas

Correct Answer: Relatively low pressures/concentrations where monolayer formation is the main process

Q30. Which pair of adsorbent properties most strongly controls adsorption capacity for organic drugs?

• Color and melting point of the adsorbent
• Surface area and pore volume/size distribution
• Thermal conductivity and electrical resistivity
• Bulk density alone

Correct Answer: Surface area and pore volume/size distribution