For 2h2 + o2 → 2h2o: 4 moles of h2 will react with moles of o2 to produce moles of h2o

The ratio is 2:1. You need two moles of hydrogen for every mol of O2. The proportion would be written as
2:1::4:x
2/1 = 4/x Cross multiply
2x = 4 Divide by 2
x = 4/2
x = 2

You would need 2 moles of O2 to react with 4 mols of H2

The answer is d) light rays pass through mirrors at an angle.

I'm sorry but, is there a list of options?