For real gases,the van der Waals equation is written as $\left( p + \frac{a n^2}{V^2} \right) (V - nb) = nRT$,where $a$ and $b$ are van der Waals constants. Two sets of gases are:
$(I)$ $O_2, CO_2, H_2, He$
$(II)$ $CH_4, O_2, H_2$
The gases given in set-$I$ are arranged in increasing order of $b$,and the gases given in set-$II$ are arranged in decreasing order of $a$. Select the correct order from the following:

• A
  $I. He < H_2 < O_2 < CO_2$; $II. CH_4 > O_2 > H_2$
• B
  $I. O_2 < He < H_2 < CO_2$; $II. H_2 > O_2 > CH_4$
• C
  $I. H_2 < He < O_2 < CO_2$; $II. CH_4 > O_2 > H_2$
• D
  $I. H_2 < O_2 < He < CO_2$; $II. O_2 > CH_4 > H_2$