21. The extent of adsorption of gases on a solid increases with:
- a) Increase in temperature
- b) Decrease in surface area
- c) Increase in critical temperature of gas
- d) Decrease in pressure of gas
Answer: c) Increase in critical temperature of gas
Explanation: Gases with a higher critical temperature are more easily liquefied and exhibit greater adsorption, as they have stronger intermolecular forces.
22. Which of the following adsorption isotherms assumes multilayer adsorption?
- a) Freundlich
- b) Langmuir
- c) BET
- d) Temkin
Answer: c) BET
Explanation: The BET isotherm extends the Langmuir model to account for multilayer adsorption, making it suitable for studying adsorption on porous surfaces.
23. Which of the following substances is commonly used as an adsorbent in gas masks?
- a) Silica gel
- b) Activated charcoal
- c) Alumina
- d) Fuller’s earth
Answer: b) Activated charcoal
Explanation: Activated charcoal is used in gas masks due to its high surface area and ability to adsorb a wide range of gases and toxic substances.
24. In adsorption from solution, the amount adsorbed depends on:
- a) Temperature only
- b) Pressure only
- c) Concentration of solute
- d) The type of solvent used
Answer: c) Concentration of solute
Explanation: In adsorption from solution, the extent of adsorption is directly related to the concentration of the solute; the greater the concentration, the greater the adsorption.
25. The process of adsorption generally:
- a) Increases the surface energy of the adsorbent.
- b) Decreases the surface energy of the adsorbent.
- c) Has no effect on the surface energy of the adsorbent.
- d) Occurs with an increase in entropy.
Answer: b) Decreases the surface energy of the adsorbent.
Explanation: Adsorption decreases the surface energy of the adsorbent because the adsorbate molecules reduce the free energy of the surface by binding to it.
26. Which of the following is not a factor affecting adsorption of gases on solids?
- a) Nature of the gas
- b) Temperature
- c) Nature of the solid
- d) External magnetic field
Answer: d) External magnetic field
Explanation: The adsorption of gases on solids is primarily influenced by the nature of the gas, temperature, and the nature of the solid adsorbent. An external magnetic field does not typically affect adsorption unless the adsorbent or adsorbate is magnetic.
27. Adsorption isotherms are useful to describe:
- a) Variation of temperature with time
- b) Variation of pressure with temperature
- c) Variation of adsorption with temperature
- d) Variation of adsorption with pressure
Answer: d) Variation of adsorption with pressure
Explanation: Adsorption isotherms describe how the extent of adsorption varies with pressure at a constant temperature. They provide insight into the surface properties of the adsorbent.
28. What happens to adsorption if the surface area of the adsorbent is increased?
- a) Adsorption increases
- b) Adsorption decreases
- c) Adsorption remains constant
- d) Adsorption depends only on temperature
Answer: a) Adsorption increases
Explanation: Adsorption increases with an increase in surface area because more surface sites are available for adsorbate molecules to adhere to.
29. Which of the following is the main driving force for physical adsorption?
- a) Chemical bonding
- b) Van der Waals forces
- c) Hydrogen bonding
- d) Covalent bonding
Answer: b) Van der Waals forces
Explanation: Physisorption is driven by weak Van der Waals forces, which are short-range, attractive interactions between the adsorbate and the surface of the adsorbent.
30. Which of the following gases would be the least adsorbed on a solid surface at room temperature?
- a) Carbon dioxide
- b) Oxygen
- c) Hydrogen
- d) Nitrogen
Answer: c) Hydrogen
Explanation: Hydrogen has a very low critical temperature and small molecular size, making it less prone to adsorption compared to gases like CO₂ or O₂.
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