Answer
$2.5\times 10^{25}/m^3$
Work Step by Step
We can determine the required number density of gas molecules as follows:
$\frac{N}{V}=\frac{pN_A}{RT}$
We plug in the known values to obtain:
$\frac{N}{V}=\frac{(101300)(6.02\times 10^{23})}{8.31\times 295}$
This simplifies to:
$\frac{N}{V}=2.5\times 10^{25}/m^3$