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
I believe it would be the last one because you can use the molar mass of HCl to find the number of moles, then use Avogadro’s number to find the number of atoms Hope this helps!
