Use of the data booklet is relevant to this question.

the approximate percentage composition of the atmosphere on four different planets is given in
the table below.

the density of a gas may be defined as the mass of 1 dm3
of the gas measured at s. t.p.

which mixture of gases has the greatest density?

planet major gases /
% by number of molecules
a jupiter h2 89.8, he 10.2
b neptune h2
80.0, he 19.0, ch4 1.0
c saturn h2 96.3, he 3.25, ch4 0.45
d uranus h2 82.5, he 15.2, ch4 2.3