Question

Given below are two statements : one is labelled as Assertion A and the other is labelled as Reason R.
Assertion A : SO$_2$(g) is adsorbed to a larger extent than H$_2$(g) on activated charcoal.
Reason R : SO$_2$(g) has a higher critical temperature than H$_2$(g).
In the light of the above statements, choose the most appropriate answer from the options given below.

• A. Both A and R are correct and R is the correct explanation of A.
• B. Both A and R are correct but R is not the correct explanation of A.
• C. A is correct but R is not correct.
• D. A is not correct but R is correct.

Hint:

For physical adsorption, a good rule of thumb is: the higher the critical temperature of a gas, the stronger the intermolecular forces, the easier it is to liquefy, and the greater its extent of adsorption on a solid surface.

Answer 1

The Correct Option is A

Let's analyze the assertion and the reason.
Assertion A: SO$_2$(g) is adsorbed to a larger extent than H$_2$(g) on activated charcoal. This is a factual statement. The extent of physisorption of a gas depends on its nature.
Reason R: SO$_2$(g) has a higher critical temperature than H$_2$(g). The critical temperature ($T_c$) is the temperature above which a gas cannot be liquefied, no matter how much pressure is applied.
$T_c$ of SO$_2$ is 430 K (157 $^\circ$C).
$T_c$ of H$_2$ is 33 K (-240 $^\circ$C).
So, the reason is also a correct factual statement.
Now, let's establish the link. The ease of liquefaction of a gas is directly related to its critical temperature. A gas with a higher critical temperature has stronger intermolecular forces and can be liquefied more easily.
Gases that are more easily liquefiable are also more readily adsorbed on the surface of a solid adsorbent (like activated charcoal).
Since SO$_2$ has a much higher critical temperature than H$_2$, it is more easily liquefiable and thus adsorbed to a much larger extent.
Therefore, both Assertion A and Reason R are correct, and Reason R is the correct explanation for Assertion A.