Calculating molarity of a gas using ideal gas equation
Hydrogen at one atmosphere pressure and 298 K is certainly not a one molar solution. However, you can still calculate the concentration with the ideal gas. Note that this is a gaseous solution and since it is a pure gas, the solute is also the solvent. 
$$
c(\ce{H2}) = \frac{n(\ce{H2})}{V(\ce{H2})} 
           = \frac{p(\ce{H2})}{\mathcal{R}T}
           \approx 40.9~\mathrm{mol\,m^{-3}}
           \approx 0.04~\mathrm{mol\,L^{-1}}
$$