Explanation

(c)
Rate of diffusion depends upon the molecular masses of gases. Therefore, the gases which have equal molecular mass, have equal rates of diffusion.
$\frac{r_{1}}{r_{2}} = \sqrt{\frac{M_{2}}{M_{1}}}$
Molecular mass of $N_{2}O = 28 + 16 = 44$
Molecular mass of ${CO}_{2} = 12 + 32 = 44$
$\because\ \frac{r_{N_{2}O}}{r_{{CO}_{2}}} = 1$
$\therefore\ \ \ r_{N_{2}O} = r_{{CO}_{2}}$