A plot of volume versus temperature (T) for a gas at constant pressure is a straight line passing through the origin. The plots at different values of pressure are shown in the figure given below.

       

The correct order of pressure is -

         Temperature (K) 

1. p1>p2>p3>p4

2. p1=p2=p3=p4

3. p1<p2<p3<p4

4. p1<p2=p3<p4