JEE Main 2022 · 29 July · evening · Single correct · +4 / −1
Given below are the critical temperatures of some of the gases:
The gas showing least adsorption on a definite amount of charcoal is
| Gas | Critical temperature (K) |
|---|---|
| He | 5.2 |
| CH₄ | 190.0 |
| CO₂ | 304.2 |
| NH₃ | 405.5 |
- (a) He
- (b) CH₄
- (c) CO₂
- (d) NH₃
Answer and solution
Answer (a) He
Solution
Chemistry ma’am · 3 steps
Higher critical temperature means an easier gas to liquefy, and that gas sticks to charcoal more.
- Link to Tc. Physical adsorption on charcoal is due to weak van der Waals forces. A gas with a higher critical temperature has stronger intermolecular forces and liquefies more easily, so it is adsorbed more.
Gas Critical temperature (K) Extent of adsorption He 5.2 least CH₄ 190.0 more CO₂ 304.2 still more NH₃ 405.5 most - Why helium. Helium has very weak dispersion forces between its small, non-polar atoms. With T_c of only 5.2 K, it is the hardest of these gases to liquefy.
- So. He shows the least adsorption on charcoal, which is option (a).
The idea to keep. For physisorption, order the gases by critical temperature: the higher the T_c, the easier the gas liquefies and the more of it charcoal adsorbs.
Answer from the NTA final answer key. Solution by PrepWiser.