How many grams of water form when 1.24 l of gas h2 at stp completely reacts with o2?

Balanced reaction for formation of water is;

2H2 + O2 - > 2H2O

Stoichiometry of H2 to H20 is 2:2

1 mol of any gas occupies a volume of 22.4 L

Therefore it 22.4 L contains 1 mole

Then 1.24 L has - 1/22.4 x 1.24 = 0.055 mol

Number of water moles formed = 0.055 mol

Therefore mass of water formed = 0.055 mol x 18 g/mol = 0.99 g of water is formed