Adsorption at solid interfaces MCQs With Answer is an essential revision tool for B. Pharm students studying surface phenomena, drug–excipient interactions, and chromatographic separations. This concise, keyword-rich introduction covers adsorption mechanisms (physisorption vs chemisorption), adsorption isotherms (Langmuir, Freundlich, BET), thermodynamics, kinetics, surface area and porosity, and pharmaceutical applications such as drug delivery, formulation stability, and purification. Understanding factors like pH, temperature, surface charge and adsorbent properties helps predict sorption behavior and design experiments. These MCQs emphasize conceptual clarity, equation interpretation, and problem-solving skills needed for exams and lab work. Now let’s test your knowledge with 50 MCQs on this topic.
Q1. What is adsorption at a solid interface?
- Accumulation of molecules in the bulk solution
- Accumulation of molecules at the solid–liquid or solid–gas boundary
- Desorption of molecules from a surface
- Covalent bonding between solvent molecules
Correct Answer: Accumulation of molecules at the solid–liquid or solid–gas boundary
Q2. Which statement best distinguishes physisorption from chemisorption?
- Physisorption involves chemical bond formation; chemisorption involves weak van der Waals forces
- Physisorption is generally reversible and involves weak forces; chemisorption is stronger and often irreversible
- Both are identical in energy and reversibility
- Chemisorption only occurs at low temperatures while physisorption requires high temperatures
Correct Answer: Physisorption is generally reversible and involves weak forces; chemisorption is stronger and often irreversible
Q3. Which isotherm assumes monolayer adsorption on a homogeneous surface?
- Freundlich isotherm
- BET isotherm
- Langmuir isotherm
- Temkin isotherm
Correct Answer: Langmuir isotherm
Q4. The Langmuir adsorption equation is best written as:
- qe = Kf Ce^(1/n)
- qe = (qmax b Ce) / (1 + b Ce)
- qe = kT ln Ce
- qe = qmax (Ce / (Ce + K))
Correct Answer: qe = (qmax b Ce) / (1 + b Ce)
Q5. In the Langmuir model, what does qmax represent?
- The Freundlich constant for adsorption intensity
- The maximum adsorption capacity corresponding to a complete monolayer
- The slope of the BET plot
- The temperature dependence of adsorption
Correct Answer: The maximum adsorption capacity corresponding to a complete monolayer
Q6. The Freundlich isotherm is best described as:
- A model assuming a single energy of adsorption for all sites
- An empirical multilayer adsorption model
- An empirical model for heterogeneous surfaces with non-uniform energies
- A kinetic rate equation for adsorption
Correct Answer: An empirical model for heterogeneous surfaces with non-uniform energies
Q7. In the Freundlich equation qe = Kf Ce^(1/n), what does a 1/n value < 1 indicate?
- Unfavorable adsorption
- Linear adsorption behavior
- Favourable adsorption with increasing capacity at higher concentration
- Complete monolayer formation
Correct Answer: Favourable adsorption with increasing capacity at higher concentration
Q8. BET theory is primarily used to determine which property of an adsorbent?
- Surface charge
- Pore size distribution
- Specific surface area by multilayer adsorption
- Thermal stability
Correct Answer: Specific surface area by multilayer adsorption
Q9. Which gas is commonly used in BET surface area measurements?
- Oxygen
- Nitrogen
- Carbon dioxide
- Methane
Correct Answer: Nitrogen
Q10. Which parameter indicates spontaneity of adsorption in thermodynamics?
- Positive ΔH
- Negative ΔG
- Zero ΔS
- Positive ΔG
Correct Answer: Negative ΔG
Q11. The relationship between Gibbs free energy change and equilibrium constant K is:
- ΔG = RT ln K
- ΔG = -RT ln K
- ΔG = ΔH – TΔS
- ΔG = ΔS / T
Correct Answer: ΔG = -RT ln K
Q12. Which factor does NOT significantly affect adsorption at solid interfaces?
- Temperature
- pH of the solution
- Molar mass of inert gas in the bulk unrelated to adsorbate
- Surface area and porosity of adsorbent
Correct Answer: Molar mass of inert gas in the bulk unrelated to adsorbate
Q13. Activated charcoal is widely used in pharmacy mainly because of its:
- Covalent binding properties
- High specific surface area and porosity
- Solubility in water
- Strong color
Correct Answer: High specific surface area and porosity
Q14. Which adsorption phenomenon is most important in chromatographic separation?
- Bulk precipitation
- Partitioning into solvent only
- Surface adsorption-desorption equilibria
- Polymerization on the stationary phase
Correct Answer: Surface adsorption-desorption equilibria
Q15. The separation factor (RL) in Langmuir is used to assess:
- Adsorption kinetic order
- Favorability of the adsorption process
- Surface area per gram of adsorbent
- Desorption activation energy
Correct Answer: Favorability of the adsorption process
Q16. A value of RL between 0 and 1 indicates:
- Unfavorable adsorption
- Favorable adsorption
- Irreversible adsorption
- No adsorption
Correct Answer: Favorable adsorption
Q17. Which kinetic model often describes chemisorption better than physisorption?
- Pseudo-first-order
- Pseudo-second-order
- Zero-order
- Michaelis-Menten
Correct Answer: Pseudo-second-order
Q18. The Lagergren pseudo-first-order kinetic equation is often linearized as:
- ln(qe – qt) = ln qe – k1 t
- t/qt = 1/(k2 qe^2) + t/qe
- qe = qmax b Ce / (1+bCe)
- ln Ce = ln C0 – kt
Correct Answer: ln(qe – qt) = ln qe – k1 t
Q19. In adsorption kinetics, qt refers to:
- Amount of adsorbate desorbed at equilibrium
- Amount of adsorbate adsorbed at time t per unit mass of adsorbent
- Total capacity of adsorbent
- Initial concentration of adsorbate
Correct Answer: Amount of adsorbate adsorbed at time t per unit mass of adsorbent
Q20. Which of the following describes chemisorption?
- Low activation energy and involving van der Waals forces
- Formation of chemical bonds and higher activation energy
- Completely independent of temperature
- Always reversible with no heat change
Correct Answer: Formation of chemical bonds and higher activation energy
Q21. Which technique can measure surface area and pore volume of pharmaceutical adsorbents?
- UV-Vis spectroscopy
- BET nitrogen adsorption
- HPLC
- Mass spectrometry
Correct Answer: BET nitrogen adsorption
Q22. Adsorption hysteresis in desorption is usually associated with:
- Ideal monolayer adsorption
- Pore structure and capillary condensation in mesopores
- Absence of pores
- Only chemisorption processes
Correct Answer: Pore structure and capillary condensation in mesopores
Q23. In batch adsorption experiments, qe is calculated from:
- Initial and equilibrium concentrations of adsorbate and mass of adsorbent
- Only the initial concentration
- Only the volume of the solution
- Temperature and pressure only
Correct Answer: Initial and equilibrium concentrations of adsorbate and mass of adsorbent
Q24. Which parameter represents adsorption intensity in the Freundlich isotherm?
- Kf
- 1/n
- qmax
- b
Correct Answer: 1/n
Q25. Which is TRUE about multilayer adsorption as per BET theory?
- It assumes a finite number of layers
- It extends Langmuir to allow multiple adsorption layers
- It is applicable only to chemisorption
- BET does not involve an equilibrium pressure term
Correct Answer: It extends Langmuir to allow multiple adsorption layers
Q26. For adsorption of weakly ionized drugs, the role of pH is important because:
- pH changes surface area of adsorbent
- pH affects drug ionization and surface charge, altering adsorption
- pH only affects desorption but not adsorption
- pH changes molar mass of the drug
Correct Answer: pH affects drug ionization and surface charge, altering adsorption
Q27. Zeta potential of an adsorbent surface helps predict:
- Thermal stability
- Electrostatic interactions and stability of colloidal dispersions
- Molecular weight distribution
- BET surface area directly
Correct Answer: Electrostatic interactions and stability of colloidal dispersions
Q28. Which model gives a linear plot of 1/qe vs 1/Ce for Langmuir isotherm?
- Freundlich linearization
- Langmuir linearization
- BET linearization
- Temkin linearization
Correct Answer: Langmuir linearization
Q29. In pharmaceutical formulation, unwanted adsorption of drug onto container surface leads to:
- Increased bioavailability
- Loss of drug potency and inaccurate dosing
- Enhanced solubility
- Reduced need for preservatives
Correct Answer: Loss of drug potency and inaccurate dosing
Q30. Which sorbent is commonly used for removing drug residues in wastewater treatment?
- Activated carbon
- Gelatin
- Sucrose
- Polyethylene glycol
Correct Answer: Activated carbon
Q31. Which thermodynamic sign suggests adsorption is exothermic?
- Positive ΔH
- Negative ΔH
- Zero ΔH
- Positive ΔS
Correct Answer: Negative ΔH
Q32. In chromatographic adsorption, retention time increases when:
- Analyte has weaker interaction with stationary phase
- Analyte has stronger adsorption to stationary phase
- Mobile phase polarity matches stationary phase exactly
- Column temperature is infinitely high
Correct Answer: Analyte has stronger adsorption to stationary phase
Q33. The Temkin isotherm accounts for:
- Adsorption heat constancy and adsorbent-adsorbate interactions with linear decrease of heat
- Only multilayer adsorption
- Only homogeneous surfaces
- Irreversible adsorption kinetics
Correct Answer: Adsorption heat constancy and adsorbent-adsorbate interactions with linear decrease of heat
Q34. Which experimental method directly studies adsorption kinetics in solutions?
- Equilibrium dialysis only
- Time-dependent batch adsorption experiments measuring qt over time
- BET surface area at a single time point
- Mass spectrometry without time sampling
Correct Answer: Time-dependent batch adsorption experiments measuring qt over time
Q35. Which equation describes pseudo-second-order kinetics in linear form?
- ln(qe – qt) = ln qe – k1 t
- t/qt = 1/(k2 qe^2) + t/qe
- qt = qmax b Ce / (1 + b Ce)
- qe = Kf Ce^(1/n)
Correct Answer: t/qt = 1/(k2 qe^2) + t/qe
Q36. What does a high value of adsorption distribution coefficient (Kd) indicate?
- Poor affinity of adsorbent for adsorbate
- High affinity and strong adsorption onto the adsorbent
- High solubility in the mobile phase only
- Low adsorption capacity regardless of concentration
Correct Answer: High affinity and strong adsorption onto the adsorbent
Q37. Which surface property increases adsorption of hydrophobic drugs from aqueous solutions?
- Highly hydrophilic adsorbent surface
- Hydrophobic adsorbent surface with nonpolar sites
- Highly charged polar sites only
- Complete lack of porosity
Correct Answer: Hydrophobic adsorbent surface with nonpolar sites
Q38. In adsorption studies, what is the main purpose of isotherm fitting?
- To determine the color of adsorbent
- To model equilibrium relationship and infer mechanism and capacity
- To measure viscosity of solution
- To calculate molecular weight of adsorbate
Correct Answer: To model equilibrium relationship and infer mechanism and capacity
Q39. Which adsorption process is most likely to increase with increasing temperature?
- Physisorption only
- Endothermic chemisorption or processes with positive ΔH
- All adsorption decreases with temperature
- BET multilayer adsorption always decreases with temperature
Correct Answer: Endothermic chemisorption or processes with positive ΔH
Q40. Which is a typical application of adsorption in pharmaceuticals?
- Drug crystal melting
- Adsorbent-mediated taste masking and impurity removal
- Increasing tablet hardness via covalent modification
- Converting liquids to gases
Correct Answer: Adsorbent-mediated taste masking and impurity removal
Q41. The Freundlich constant Kf is related to:
- Adsorption capacity at unit concentration
- Activation energy of adsorption
- Pore volume exclusively
- Surface roughness only
Correct Answer: Adsorption capacity at unit concentration
Q42. Which is true about multilayer adsorption before capillary condensation?
- It only occurs in micropores smaller than 2 nm
- BET theory models adsorption up to relative pressures where capillary condensation may begin
- It contradicts all experimental isotherms
- It is irrelevant to surface area measurements
Correct Answer: BET theory models adsorption up to relative pressures where capillary condensation may begin
Q43. Which analysis helps distinguish between physical and chemical adsorption?
- Comparing activation energy and temperature dependence; chemisorption shows higher activation energy
- Measuring color change only
- Viscosity measurements of the solution
- Counting particles under microscope
Correct Answer: Comparing activation energy and temperature dependence; chemisorption shows higher activation energy
Q44. In fixed-bed adsorption columns, breakthrough curve analysis helps determine:
- Equilibrium piezoelectric constants
- Column capacity, breakthrough time and design parameters
- Only the BET surface area
- Thermal conductivity of stationary phase
Correct Answer: Column capacity, breakthrough time and design parameters
Q45. Which statement about adsorption-desorption cycles is correct?
- Adsorption and desorption are always symmetric
- Inefficient desorption may indicate strong chemisorption or pore trapping
- Desorption efficiency is independent of temperature
- Once adsorbed, molecules cannot be desorbed under any conditions
Correct Answer: Inefficient desorption may indicate strong chemisorption or pore trapping
Q46. Which factor would increase adsorption of a cationic drug onto an adsorbent?
- Negative surface charge on adsorbent at formulation pH
- Positive surface charge on adsorbent
- Strongly hydrophilic neutral surface only
- Absence of any surface functional groups
Correct Answer: Negative surface charge on adsorbent at formulation pH
Q47. Which adsorption isotherm can be linearized by plotting log qe vs log Ce?
- Langmuir isotherm
- Freundlich isotherm
- BET isotherm
- Temkin isotherm
Correct Answer: Freundlich isotherm
Q48. When designing an adsorbent for taste masking, the key properties to optimize are:
- Low surface area and high solubility
- High surface area, appropriate pore size and favorable adsorption affinity
- High volatility and low adsorption strength
- Only thermal conductivity
Correct Answer: High surface area, appropriate pore size and favorable adsorption affinity
Q49. Which equation relates the amount adsorbed to concentration in Henry’s law region (very low concentration)?
- qe = Kd Ce (linear proportionality, Henry’s law)
- qe = qmax b Ce / (1 + b Ce)
- ln qe = ln Kf + (1/n) ln Ce
- BET multilayer equation
Correct Answer: qe = Kd Ce (linear proportionality, Henry’s law)
Q50. Which property of an adsorbent most directly enhances rapid uptake kinetics for small drug molecules?
- Very large particle size and long diffusion paths
- High external surface area and accessible pore network
- Complete hydrophobicity irrespective of drug polarity
- Low porosity and dense structure
Correct Answer: High external surface area and accessible pore network
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