> A "mole" is a unitless quantity. Literally it's just a number. True, but it's defined relative to the kg. It's the quantity of Carbon-12 atoms in 12g of Carb

> A "mole" is a unitless quantity. Literally it's just a number. True, but it's defined relative to the kg. It's the quantity of Carbon-12 atoms in 12g of Carbon-12. As for why it isn't an 'simpler' number, it's because if you want a standardized definition of something you have to have a reliable reference. Which is precisely why the kg itself is being redefined. Side-note: the act of creating this ultra-pure kg of Si-28 has actually created a lot of useful science in its own right, which is nice.