Assertion: The ratio ${\mathrm{C}}_{\mathrm{p}}/{\mathrm{C}}_{\mathrm{v}}$ for a diatomic gas is less than that for a monoatomic gas.
Reason: The molecules of a monoatomic gas have less degree of freedom than those of a diatomic gas.
 

Diatomic Gas : $\mathrm{f}=5 ; \frac{{\mathrm{C}}_{\mathrm{P}}}{{\mathrm{C}}_{\mathrm{V}}}=\frac{\mathrm{f}+2}{\mathrm{f}}=\frac{7}{5}=1.4$

Monoatomic Gas : $\mathrm{f}=3 ; \frac{{\mathrm{C}}_{\mathrm{P}}}{{\mathrm{C}}_{\mathrm{V}}}=\frac{\mathrm{f}+2}{\mathrm{f}}=\frac{5}{3}=1.67$

Thus, the ratio ${\mathrm{C}}_{\mathrm{p}}/{\mathrm{C}}_{\mathrm{v}}$ for a diatomic gas is less than that for a monoatomic gas.

The molecules of a monoatomic gas have less degree of freedom than those of a diatomic gas.