Which of the following rules should you follow to balance chemical equations? a. change only the subscripts
b. use the smallest possible subscripts
c. add coefficients as needed
d. two of the above​

c. add coefficients as needed

Explanation:

A chemical equation is defined as the equation that shows changes in a chemical reaction. A chemical equation consist of reactant and product, reactant is at left side of the arrow and product is at right side of the arrow.

Reactant => Product

While balancing a chemical equation, the basic rule is to balance the coefficient as required. Coefficient represents the number of molecules and is used at front of a chemical symbol. Change in coefficient helps balance the number of atoms or molecules of the substances on both the sides of the arrow.

Subscripts are never allowed to change because it can change the chemical involved in the reaction.

Hence, the correct answer is "c. add coefficients as needed".