The number of moles of hydrogen that is needed to produce 0.253 mol of water

The balanced equation that describes the reaction between hydrogen and oxygen to produce water is 2 H2+O2= 2H2O. Hence to produce 2 moles of water 2 moles of hydrogen is equivalently needed. For the given, 0.253 moles water thus needs 0.253 moles of hydrogen, too.