The volume of dry hydrogen gas at standard atmospheric pressure (which is typically defined as 1 atm or 101.325 kPa) depends on the number of moles of hydrogen gas present. The ideal gas law, PV = nRT, relates the pressure (P), volume (V), number of moles (n), and temperature (T) of an ideal gas. Assuming standard temperature and pressure (0°C and 1 atm), one mole of any ideal gas occupies a volume of 22.4 L. Therefore, to find the volume of dry hydrogen gas at standard atmospheric pressure, we need to know how many moles of hydrogen gas we have.
For example, if we have 1 mole of dry hydrogen gas at standard atmospheric pressure, the volume would be 22.4 L. If we have 0.5 moles of dry hydrogen gas, the volume would be 11.2 L. And so on.