For real gases, van der Waals' equation is written as
`(P+(an^(2))/(V^(2))) (V-nb)= nRT`
where `a` and `b` are van der Waals' constants.
Two sets of gases are:
`(I) O_(2), CO_(2), H_(2)` and `He(II) CH_(4), O_(2)` and `O_(2) and H_(2)`
The gases given in set `I` in increasing order of `b` and gases given in set `II` in decreasing order of `a` are arranged below. Select the correct order from the following :

Options

A. (I) `He lt H_(2) lt CO_(2) lt O_(2)` , (II) `CH_(4) gt H_(2) gt O_(2)`
B. (I) `O_(2) lt He lt H_(2) lt CO_(2)` , (II) `H_(2) gt O_(2) gt CH_(4)`
C. (I) `H_(2) lt He lt O_(2) lt CO_(2)` , (II) `CH_(4) gt O_(2) gt H_(2)`
D. (I) `H_(2) lt O_(2) lt He lt CO_(2)` , (II) `O_(2) gt CH_(4) gt H_(2)`.

Answer

C

Explanation

van der Waals constant 'a' reprsents intermolecular forces of attraction in the gaseous molecules. The increasing order of attractive force in set (I) is :
`H_(2) lt He lt O_(2) lt CO_(2)`
van der Waals' constant 'b' represents molecular size or molecular volume. The decreasing order of molecular volume is :
`:.` (c ) is the correct order.