The mole is the unit used to measure which quantity?

1. Chemists often need to know how many particles are present rather than what they weigh. 2. The amount of substance is so important that it is given its own name, the mole. 3. The mole is a counting unit, in the same way that a dozen or an hour is a counting unit. _Source: Siyavula Physical Sciences Grade 10 (Everything Science, CC BY 4.0), Chapter 19: Quantitative aspects of chemical change_