The correct answer is four.Important PointsWhen the process of formation of hydrogen by passing steam over red hot iron is presented in the form of a balanced chemical equation, then the number of water molecules on the left hand side of the equation is four.Iron is found to react with steam when it is red hot.Balanced Chemical equation \(3Fe\left( s \right) + 4{H_2}O\left( g \right) \to F{e_3}{O_4}\left( s \right) + 4{H_2}\left( g \right)\)Theoretically, the reaction of red hot iron with steam is a reversible reaction.But in practice, the reaction proceeds continuously from reactants to products because the hydrogen is blown out of contact with iron by the force of the current of the steam.