Answer
$\frac{N}{V} = 2.69\times 10^{25}~m^{-3}$
Work Step by Step
We can calculate the Loschmidt number:
$PV = NkT$
$\frac{N}{V} = \frac{P}{kT}$
$\frac{N}{V} = \frac{(1.015\times 10^5~N/m^2)}{(1.38\times 10^{-23}~J/K)(273~K)}$
$\frac{N}{V} = 2.69\times 10^{25}~m^{-3}$
