Answer
$M=15.64g/mol$
Work Step by Step
We can find the required molecular mass as follows:
$PV=nRT$
$\implies n=\frac{PV}{RT}$
We plug in the known values to obtain:
$n=\frac{(153\times 10^3)(515\times 10^{-6})}{(8.314)(322)}$
$n=2.94\times 10^{-2}$
Now the molecular mass is given as
$M=\frac{0.460}{2.94\times 10^{-2}}$
$M=15.64g/mol$