Given var der Waals constant for $NH_3, H_2, O_2$ and $CO_2$are respectively 4.17, 0.244, 1.36 and 3.59, which one of the following gases is most easily liquefied ?

Question

( A ) $H_2$
( B ) $O_2$
( C ) $NH_3$
( D ) $CO_2$