From ideal gas equation
$pV = nRT $
where $p$ is pressure,
$V$ the volume,
$R$ the gas constant,
$T$ the temperature and
$n$ the number of moles.
$\therefore n=\frac{p V}{R T}$
Given $ p =22.4\, atm$ pressure
$=22.4 \times 1.01 \times 10^{5} Nm ^{-2}$
$V=2 L=2 \times 10^{-3} m ^{3}$
$ R=8.31 \,J\,mol ^{-1}- K ^{-1}$
$ T =273 \,K$
$\therefore n=\frac{22.4 \times 1.01 \times 10^{5} \times 2 \times 10^{-3}}{8.31 \times 273}$
$ n=1.99 \approx 2$
$\therefore n=\frac{\text { mass }}{\text { atomic weigh }}$
We have mass $=n \times$ atomic weight
$=2 \times 14=28 \,g$