c
(c)
Degrees of freedom of $He \left(f_{ He }\right)=3$
Degrees of freedom of $O _2\left(f_{ O _2}\right)=5$
Degrees of freedom of $O _3\left( f _{ O _3}\right)=6$
$n_{ He }=2, \quad n_{ O _2}=4 \quad n_{ O _3}=1$
Energy of mixture = Sum of individual energies
$=\left(n_{ He}f_{ He }+n_{ O _2} f_{ O _2}+n_{ O _3} f_{ O _3}\right) \frac{R T}{2}$
$=(2 \times 3+4 \times 5+1 \times 6) \frac{R T}{2}$
$=(3+10+3) R T$
$=16 R T$