At $27^{\circ} \mathrm{C}$, the osmotic pressure of a solution containing $4 \mathrm{~g}$ of a non-electrolyte solute in $1.0 \mathrm{~L}$ of solution is $0.4 \mathrm{bar}$. The molar mass of the solute in $\mathrm{g} \mathrm{mol}^{-1}$ is :
$\left(\mathrm{R}=0.083 \mathrm{Lbar} \mathrm{K}^{-1} \mathrm{~mol}^{-1}\right)$