Answer
Elements are made of atoms, which can neither be created nor destroyed. All atoms of the same element will have the same properties and cannot change to become another element. Because atoms cannot be broken down or added upon to form new elements, all chemical reactions must have conserved mass and sampled substances must have consistent ratios of elements within them.
Work Step by Step
Since atoms cannot be created or destroyed, the mass of matter before and after a chemical reaction must be the same. Since atoms cannot change their elemental identity, the types and amount of elements present in a reaction or sampled compounds must always be consistent.
