For real gases the relation between p, V and T is given by c=van der Waal's equation
`(p+ (an^(2))/V^(2)) (V-nb)=nRT`
where, 'a' and 'b' are van der Waal's constanrs, 'nb' is approximately equal to the total volume of the molecules of a gas. 'a' is the measure of magnitude of intermolecular attraction.
(i) Arrange the following gases in the increasin order of 'b'. give reason.
`O_(2), CO_(2), H_(2), He`
(ii) Arrange the following gases in the decreasing order of magnitude of 'a'. Give reason.
`CH_(4), O_(2), H_(2)`

Explanation

(i) As nb is approximately equal to the total volume of the gas, its magnitude depends upon the size of the gas molecules. The increasing order of 'b' is `H_(2) lt He lt O_(2) lt CO_(2)` since molecular size increases in this order.
(ii) As 'a' depends upon the intermolecular force of attraction, the decreaing order of magnitude of 'a' is : `CH_(4) gt O_(2) gt H_(2)`. These force are the maximum in `CH_(4)` because intermolecular forces are linked to the surface area of size of the molecules in gas.