b
For ideal gas
$P V=n R T$
$P V=\frac{m}{M} R T$
$P=\left(\frac{M}{V}\right) \frac{R T}{M}$
$P=\frac{\rho R T}{M}$
(Where $\mathrm{m}$ is mass of gas and $\mathrm{M}$ is molecular mass of gas)
for same temperature $\mathrm{P}_1>\mathrm{P}_2>\mathrm{P}_3$
So $\rho_1>\rho_2>\rho_3$
So correct answer is $(2)$
