If ten volumes of dihydrogen gas reacts with five volumes of dioxygen gas, how many volumes of water vapour would be produced?

The balanced chemical equation for the reaction is, 2H₂ + O₂ → 2H₂O. The volume of a gas is directly proportional to the number of moles. Thus, 2 volumes of dihydrogen react with 1 volume of oxygen to form 2 volumes of water. Thus, 10 volumes of dihydrogen react with 5 volumes of oxygen to form 10 volumes of water.