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 'b' represents molar volume occupied by the gas molecules, greater the size of the molecules, greater is the volume occupied by 1 mole of molecules. The size and hence the value of 'b' increase in the order :
`H_(2) lt He lt O_(2) lt CO_(2)`
(ii) As all the given molecules are non-polar, the magnitude of intermolecular attractions and hence the value of 'a' increase with the increase in number of electrons in the molecule, i.e., in the order :
`CH_(4) gt O_(2) gt H_(2)`
(Greater the number of electrons, greater is the size of electron cloud, greater is the polarisation of the molecule, greater is the attraction).