Which law tells us the number of atoms of each element must be the same on both sides of a chemical equation?

I think the law in question here is the law of conservation of mass. All chemical equations have to adhere to the law of conservation of mass, that states that matter cannot be created or destroyed; thus, there must be the same number of atoms of each element on each side (right and the left side)of the chemical equation.

Crust,mantle,core,earth

Contained in chromosomes which are located in the nucleus of the cell.