If an equation is balanced properly, both sides of

the equation must have the same number of

(1) atoms

(2) coefficients

(3) molecules

(4) moles of molecules

In chemistry, to determine whether a equation is balanced or not, it needs to have the same number of atoms. Because sometimes, you can include subscripts and no coefficients. Also, in the law of conversation of mass, no matter can be created nor destroyed in a reaction, so all equations must be balanced.

Final answer: - (1) atoms