Question

Assertion:-Solids in finely divided state act as good adsorbents.
Reason:-Adsorption is a surface phenomenon.
(A) Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
(B) Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
(C) Assertion is correct but Reason is incorrect
(D) Both Assertion and Reason are incorrect

Answer 1

Approach this question by checking both the statements given in the question, whether they are true or false followed by checking, whether the reason given is valid for the assertion statement or not. As we know that adsorption is defined as the adhesion of atoms, ions or molecules from a gas, liquid or dissolved solid to a surface.

Complete answer:
Let us check both the statements one by one as follows:-
-Solids in finely divided state act as good adsorbents:-
As we know that surface area is of the factors on which extent of adsorption depends, that is adsorption is directly proportional to the surface area of the solid. Increase in the surface area of the adsorbent increases the total amount of gas being adsorbed on it. Finely divided solids like nickel, platinum & porous substances like charcoal, silica gel etc. provides large surface area due to which both physisorption and chemisorption increase. Therefore solids in a finely divided state act as good adsorbents.
-Adsorption is a surface phenomenon:-
We know that adsorption is the phenomenon of accumulation of a large number of molecular species at the surface of liquid or solid phase in comparison to the bulk and this process occurs due to presence of unbalanced or residual forces at the surface of liquid or solid phase.
-From the above data we can see that both the statements are correct but the reason given in the question for assertion is not valid as the right reason behind it is the increment in the surface area which leads to higher adsorption.

Hence the correct option is: (B) Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion .

Note:
-Remember that the other factors which affects the rate of adsorption are as follows:-
(i) Nature and surface area of the adsorbent
(ii) Nature of the adsorbed gas
(iii) Temperature
(iv) Pressure of the gas