Question

What does elementary entities means?

Answer 1

Any countable object or event, but usually a molecule, an ion or a specified group of atoms

Amount of substance is a standards-defined quantitythat measures the size of an ensemble of elementary entities, such as atoms, molecules, electrons, and other particles. It is sometimes referred to as chemical amount. The International System of Units (SI) defines the amount of substance to be proportional to the number of elementary entities present. The SI unit for amount of substance is the mole. It has the unit symbol mol. The proportionality constant is the inverse of the Avogadro constant.