Question

How many liters of oxygen gas are required to react completely with 1.2 liters of hydrogen gas to form water?

Answer 1

Answer should be: 0.6 L

Hope this helps!

Answer 2

2H2 + O2 ----> 2H2O
2 mol 1 mol
1.2 L x L

For gases under the same conditions we can write
2 mol H2 / 1 mol O2 = 1.2 L H2 / x L O2

x=1.2*1/2=0.6 L O2