What is the coefficient for hydrogen in the balanced equation for the reaction of solid iron(iii) oxide with gaseous hydrogen to form solid iron and liquid water?

First, we must represent the compounds into their condensed formula. The reactants would be Fe2O3 and H2, then the products would be Fe and H2O. Balancing the reaction, the overall reaction would look like this:

Fe2O3 + 3H2 = 2Fe + 3H2O

Thus, the coefficient for Hydrogen gas is 3.