How many moles of hydrogen would be required to produce 5.0 mol of water?

First we need an equation:

2H*2 + 0*2 - - > 2H*2O

The ratio of hydrogen to water is

2:2 (looking at the coefficients of the substances)

This simplified gives us 1:1.

If we have 5 moles of water, the ratio 1:1, must mean we have 5 moles of hydrogen too.

Formula for water is H20 and there are 5 mol water. 2 mol of hydrogen per 1 mol water so 5 mol of water times 2 mol hydrogen will give you 10 mol of hydrogen.

Same process with oxygen except 1 mol of oxygen per mol of water. So 5 mol water times 1 mol of oxygen will give you 5 mol of oxygen.