the substances that are present before any chemical reaction are called dioxides oxygen products reactants

the substances that are present before any chemical reaction are called dioxides oxygen products reactants

the substances that are present before any chemical reaction are called dioxides oxygen products reactants

Answer

Brief Explanations:

In a chemical reaction, reactants are the starting - substances. Dioxides are a type of compound, oxygen is an element, and products are the substances formed after the reaction.

Answer:

D. reactants