What is a Mole? A Fixed Avogadro Constant Or a Fixed Carbon-12 Molar Mass: Which One to Choose?(Old Concepts and New‪)‬

In a recent issue of Chemistry International, Ian Mills and Martin Milton suggested a new definition for the mole, one of the seven base units. (1) This matter is controversial and needs a careful examination. The IUPAC Green Book (2) describes the seven base units and gives their definitions. They are the length unit, the metre; the time unit, the second; the mass unit, the kilogram; the current unit, the ampere; the temperature unit, the Kelvin; the amount of substance unit, the mole; and the luminous intensity unit, the candela. Some of them require the help of another base unit: for instance, the time unit involves the length unit, the current unit involves the length unit, and the amount of substance unit involves the mass unit.