3O₂ + 2H₂S -----------> 2SO₂ + 2H₂O
3 : 2 : 2 : 2
3 mole of oxygen gas will react with 2 moles of hydrogen sulphide gas...
x mole of oxygen gas will react with 0.45 moles of hydrogen sulphide gas...
Cross multiply
2x = 3 × 0.45
x = 0.675...
That is 0.675 mole of oxygen gas will react with 0.45 moles of hydrogen sulphide gas...
But the question days how many grams of oxygen gas and not how many moles of oxygen gas...
So we need to calculate the number of grams in their given mole...
Number of moles = reacting mass /molar mass
0.675 = Mass/32
Mass = 0.675 × 32
Mass = 21.6gramms...
Hope this helped...?