Question

3/10 substances present at the start of a chemical reaction reactants products coefficients subscripts

Explanation:

In a chemical reaction, reactants are the substances that exist at the beginning of the reaction and undergo change to form products. Products are the substances formed at the end. Coefficients are numbers in front of formulas to balance equations, and subscripts indicate the number of atoms in a molecule. So the substances at the start are reactants.

Answer:

A. reactants (assuming the first option is labeled A, but based on the content, the correct term is "reactants" corresponding to the first blue box labeled "reactants")