For real gases the relation between p, V and T is given by van der Waals equation: 

where 'a' and are van der Waals constants, '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 increasing order of 'b'. Give reason. O₂, CO₂,  H₂, He

II. Arrange the following gases in the decreasing order of magnitude of ‘a’. Give reason. CH₄, O₂, H₂. 

<p><span data-teams="true">This is a short answer type question as classified in NCERT Exemplar</span></p><p><strong>&nbsp;</strong><strong>I.</strong>The increasing order of&nbsp; ‘b’ of the given gases is:</p><p>H₂ &lt;&nbsp; He &lt;&nbsp; O₂&nbsp; &lt; CO₂</p><p>Volume of a gas is proportional to the size of the molecule.</p><p><strong>II.</strong>The decreasing order of magnitude of ‘a’ of the given molecule is:</p><p>CH₄&nbsp; &gt;&nbsp; O₂&nbsp; &gt;&nbsp; H₂&nbsp;</p><p>The Van there waals constant ‘a’ represents the magnitude of intermolecular attraction which increases with increase in the size of the electron cloud&nbsp;of the molecule. So the greater the size of a molecule, greater will be the electron cloud and hence greater will be the polarizability and more will be the magnitude of intermolecular attraction.</p>

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