H₂S gas burns in the presence of O₂ to form SO₂ and H₂O
complete reaction is as follows
2H₂S + 3O₂ ---> 2SO₂ + 2H₂O
stoichiometry of H₂S to SO₂ is 2:2
Avagadros law states that volume of gas is proportional to number of moles of gas. Therefore volume ratio between reactants and products is equal to the molar ratio.
hence, volume ratio of H₂S to SO₂ is 2:2
2 L of H₂S forms 2 L of SO₂
therefore 121 L of H₂S forms 121 L of SO₂
volume of SO₂ produced is 121 L