Which quantity or quantities must always be the same on both sides of a chemical equation? (a) the number of atoms of each kind (b) the number of molecules of each kind (c) the number of moles of each kind of molecule (d) the sum of the masses of all substances involved?

The quantities which must always be the same on both sides of a chemical equation is:

(a) the number of atoms of each kind.

(d) the sum of the masses of all substances involved.

A chemical reaction refers to a chemical process that involves the rearrangement or transformation of the ionic, atomic or molecular structure of a chemical element through the breakdown and formation of chemical bonds in order to produce a new compound.

A chemical equation is typically used to denote or represent a chemical reaction between two or more chemical elements.

A balanced chemical equation is one in which the number of atoms on the reactant (left) side is equal to the number of atoms on the product (right) side.

This ultimately implies that, both the charge on each atom and sum of the masses of the chemical substances in a chemical equation are properly balanced.

Additionally, all chemical equations must be in accordance with the Law of Conservation of Mass because mass can neither be created nor destroyed.

Read more: link