At 273°C and 380 torr pressure, the density of a gas is 1.25 kg/m³. So its density at STP in g/l is

$$\begin{gathered} \mathrm{At} \mathrm{STP}: {\mathrm{T}}_2=273\mathrm{K} \\ {\mathrm{P}}_2={10}^5\mathrm{Pa} \\ {\mathrm{\rho }}_1=1.25\mathrm{kg}/{\mathrm{m}}^3 \\ \mathrm{We} \mathrm{know} \mathrm{that} \mathrm{PV}=\mathrm{nRT} \\ \mathrm{P}=\mathrm{\rho RT} \\ \frac{{\mathrm{P}}_1}{{\mathrm{P}}_2}=\frac{{\mathrm{\rho }}_1{\mathrm{T}}_1}{{\mathrm{\rho }}_1{\mathrm{T}}_2} \\ \Rightarrow {\mathrm{\rho }}_2={\mathrm{\rho }}_1\frac{{\mathrm{T}}_1}{{\mathrm{T}}_2}\frac{{\mathrm{P}}_2}{{\mathrm{P}}_1} \\ {\mathrm{\rho }}_2=1.25\times \frac{546}{273}\times \frac{{10}^5}{5.06\times {10}^4} \\ {\mathrm{\rho }}_2=4.94\mathrm{kg}/{\mathrm{m}}^3 \\ {\mathrm{\rho }}_2=4.94\mathrm{g}/\mathrm{l} \\ {\mathrm{\rho }}_2\approx 5\mathrm{g}/\mathrm{l} \end{gathered}$$