When hydrogen gas is passed over heated copper (II) oxide, copper and steam are formed.  State the substance reduced in this reaction.                                                                                                                                            

By verifying that both the reactant side and the product side have the same amount of atoms of each element, the balanced chemical reaction can be expressed.
While oxidation involves either acquiring hydrogen or losing oxygen, reduction involves either gaining hydrogen or losing oxygen. Redox reactions are those in which oxidation and reduction occur concurrently. By examining the shift in each element's oxidation state, we may also identify the chemicals that are being reduced and oxidized. While elements that are reduced have their oxidation states reduced, those that are oxidized reach a higher oxidation state.

The reaction between cuprous oxide and hydrogen is as follows;

${\mathrm{Cu}}_2\mathrm{O}+{\mathrm{H}}_2\to \mathrm{Cu}+{\mathrm{H}}_2\mathrm{O}$

Reduction is the process of receiving electrons. Cu has a +2 oxidation state in oxide form and it is decreased to zero in its atomic state. Thus copper is the element reduced in this reaction.

Hence, option A is correct.