Which statement correctly describes the mole?

• A. The unit amount of substance
• B. The mass of one mole of atoms
• C. The number of molecules in a sample
• D. The mass of carbon-12 in a sample

Answer: (C)

The mole is a unit of amount of substance. It tells you how many elementary entities are present, not the mass. By definition, one mole contains 6.022 × 10^23 of those entities, whether they are atoms, molecules, ions, or other particles. This means the mole is a counting unit, like a dozen, but applicable to any substance.

The mass you get from a sample comes from multiplying the amount (in moles) by the molar mass of that substance. For example, carbon-12 has a molar mass of 12 g per mole, so one mole of carbon-12 would have a mass of 12 g. But the mole itself isn’t a mass; it’s the amount that connects mass, number of particles, and molar mass. The number of molecules in a sample depends on how many moles you have, not on the mole by itself.