Answer
$2.51\times 10^5\frac{g}{mol}$
Work Step by Step
As we know that
$M=\frac{\pi}{RT}$
We plug in the known values to obtain:
$M=\frac{0.745torr\times \frac{1atm}{760torr}}{0.08206\frac{L.atm}{mol.K}\times 300K}=3.98\times 10^{-5}\frac{mol}{L}$
Now we can find the molar mass
$Molar\space mass=\frac{1.00g}{1.00L\times \frac{3.98\times 10^{-5}}{1L}}=2.51\times 10^5\frac{g}{mol}$
