Asubstance that undergoes a change in a chemical reaction is
a. a product.
c. a reactant.
b. a chemical.
d. an enzyme.

Option c. A substance that undergoes a change in a chemical reaction is a reactant.

Explanation:

In chemistry, a reactant is defined as a substance that takes part or undergoes a change during a chemical reaction in order to make a product. Some chemical reactions go to completion, which means that all reactants participating in that reaction become products. These type of chemical reactions are called irreversible. Other reactions do not go into completion, and there is a balance between the amount of reactants and products left, these reactions are called reversible.

a) the particles of the chair are strongly held together.