Question

Given below are the critical temperatures of some of the gases :

Gas	Critical temperature (K)
He	5.2
CH4	190.0
CO2	304.2
NH3	405.5

The gas showing least adsorption on a definite amount of charcoal is

• A. He
• B. CH₄
• C. CO₂
• D. NH₃

Answer 1

The Correct Option is A

To determine which gas shows the least adsorption on charcoal, we need to understand the concept of adsorption in gases. Adsorption is a surface phenomenon where gases accumulate on the surface of a solid. The amount of adsorption is influenced by several factors, including the critical temperature of the gases.

1. The critical temperature of a gas is the temperature above which it cannot be liquefied, regardless of the pressure applied. Gases with higher critical temperatures are more easily adsorbed because they are closer to their liquefaction point and have stronger intermolecular forces.
2. From the given table, the critical temperatures of the gases are:
   • He (Helium): 5.2 K
   • CH₄ (Methane): 190.0 K
   • CO₂ (Carbon Dioxide): 304.2 K
   • NH₃ (Ammonia): 405.5 K
3. Helium has the lowest critical temperature at 5.2 K, indicating it has weak intermolecular forces and is farthest from its liquefaction point under normal conditions. Therefore, it is the least adsorbed on charcoal.
4. On the other hand, NH₃ with the highest critical temperature has strong intermolecular forces and would be adsorbed the most.

Based on this reasoning, the gas showing the least adsorption on a definite amount of charcoal is Helium (He).