The balanced chemical equation for the reaction of hydrogen and oxygen is shown below. the number of moles of hydrogen that is needed to produce 0.253 mol of water is

a) 0.253

Explanation:

2H₂ + O₂ ⟶ 2H₂O

We want to convert moles of H₂O to moles of H₂.

Choose the conversion factor (the correct molar ratio)

It is or either 2 mol H₂/2 mol H₂O or 2 mol H₂O/2mol H₂

We choose the one with the desired units (mol H₂) on top.

Moles of H₂ = 0.253 mol H₂O × 2 mol H₂/2 mol H₂O

Moles of H₂ = 0.253 mol H₂