Four gases A, B, C and D have critical temperatures 5.3,33.2,126.0 and 154.3 K respectively. For their adsorption on a fixed amount of charcoal, the correct order is:

Solution

Chemistry ma’am · 4 steps

On charcoal, the gas that liquefies most easily sticks the most, so just rank by critical temperature.

1. Physical adsorption. Gases adsorb on charcoal mainly by physisorption. Weak van der Waals forces hold the gas molecules on the surface.
2. Role of critical temperature. A higher critical temperature means stronger van der Waals forces between the molecules, so the gas liquefies more easily. Such a gas is also held more strongly on a surface, so higher critical temperature means more adsorption.
3. Rank the gases. The critical temperatures are D (154.3 K) > C (126.0 K) > B (33.2 K) > A (5.3 K). These values match O₂, N₂, H₂ and He, and that is the known order of their adsorption on charcoal.
4. So. The extent of adsorption follows the critical temperatures: D > C > B > A, which is option (a).

The idea to keep. Easily liquefiable gases (higher critical temperature, stronger van der Waals forces) are physisorbed more. So NH₃, SO₂ and CO₂ adsorb far more than H₂ or He.

Answer from the NTA final answer key. Solution by PrepWiser.