Answer
$64.11347\frac{g}{mol}$
Work Step by Step
We know that
$PV=nRT$
$\implies n=\frac{PV}{RT}$
$n=\frac{0.862\times 1}{0.0820\times 298}=0.03525mol$
We can find the molar mass as
$molar mass=\frac{2.26g}{0.03525mol}=64.11347\frac{g}{mol}$