a and b are vander Waals' constants for gases. Chlorine is more easily liquefied than ethane because
(a) a and b for Cl2>a and b for C2H6
(b) a and b for Cl2<a and b for C2H6
(c) a for Cl2 >a for C2H6 but b for Cl2 >b for C2H6
(d) a for Cl2 >a for C2H6 but b for Cl2 < b for C2H6