At standard temperature and pressure conditions, 1 mol of any gas occupies a volume of 22.4 L. This is known as molar volume.
1 mol of H₂ gas occupies a volume of 22.4 L
Molar volume - 22.4 L/mol
Therefore an amount of 0.056 mol of H₂ takes up - 22.4 L/mol x 0.056 mol
Therefore volume used by 0.056 mol of H₂ - 1.25 L
