Final answer:
In the reaction where methane and oxygen turn into carbon dioxide and water, methane and oxygen are called reactants. They are listed on the reactant side of the balanced chemical equation, which is CH4 + 2O2 → CO2 + 2H2O.
Step-by-step explanation:
In the reaction where methane + oxygen turns into carbon dioxide + water, the substances methane and oxygen are called reactants. The reactant side of a chemical equation is always placed on the left side, depicting the substances that are consumed in a reaction. The product side, which comes after the arrow, shows the new substances formed as a result of the reaction, in this case, carbon dioxide and water. Therefore, for the options provided, the correct answer is (a) Reactants. The balanced chemical equation is: CH4 + 2O2 → CO2 + 2H2O.