From the equation for burning of hydrogen and oxygen
2H2 + O2 ⟶ 2H2O (Steam)
Write down the number of mole (or moles) of steam obtained from 0.5 moles of oxygen.
2H2+O2⟶2H2O2 mole1 mole2 mole\begin{matrix} 2\text{H}_2 & + &\text{O}_2 & \longrightarrow & 2\text{H}_2\text{O} \\ 2\text{ mole} & & 1\text{ mole}& & 2\text{ mole} \end{matrix}2H22 mole+O21 mole⟶2H2O2 mole
1 mole of oxygen gives 2 moles of steam
∴ 0.5 mole of oxygen will give 21\dfrac{2}{1}12 × 0.5
= 1 mole of steam
