When you balance a chemical equation, what are you doing?

A. applying the law of conservation of energy

B. applying Mendeleev's law

C. applying the law of conservation of matter

D. applying the periodic law

Answer is (C) - applying the law of conservation of matter.

Law of conservation of matter says matter can't be created or destroyed. Only thing can do is conservation.

Hence, in a chemical reaction, number of atoms of each element in reactants should be same as the number of atoms of each element in products.

When you balance a chemical equation, you are applying the law of conservation of matter. The correct answer is C.