1 mole of any gas occupies 22.4 L volume. The molecular weight of water is 18 grams. Thus 18 gram of Water will also occupy 22.4 L.We know that at STP one mole of any gas occupies 22.4litres . It means that one mole of hydrogen also occupies 22.4litres of volume at STP. So 10moles of hydrogen gas will occupy =22.4×10=224litres of volume at STP.