The density of a gas at normal pressure and $27^{\circ} C$ or $300 K$ temperature $=24$

then the density at $127^{\circ} C$ on $400 K$, pressure is constant,

So. We know,

$d=\frac{P M}{R T}$

$d \propto \frac{1}{T}$

$\Rightarrow  \frac{d_{1}}{d_{2}} =\frac{T_{2}}{T_{1}}$

$\Rightarrow  d_{2} =\frac{24 \times 300}{400}$

$d_{2} =18$

Thus, density at $127^{\circ} C , 18$ option $(c)$ is correct.