A gaseous mixture contains equal number of hydrogen and nitrogen molecules. Specific heat measurements on this mixture at temperature below $150 \mathrm{~K}$ would indicate the value of $\gamma=C_{p} / C_{V}$ for the mixture as
(a) $3 / 2$
(b) $4 / 3$
(c) $5 / 3$
(d) $7 / 5$