The number of carbon atoms in exactly 12 g of pure carbon-12 is called a:

• A. Avogadro constant
• B. molarity
• C. mole
• D. atomic mass unit

Answer: (C)

Verified step by step guidance

1. Understand that the problem is asking for the name of the quantity that represents the number of carbon atoms in exactly 12 grams of pure carbon-12.
2. Recall that 12 grams of carbon-12 contains exactly one mole of carbon atoms by definition.
3. Recognize that a 'mole' is the unit used to count a specific number of particles (atoms, molecules, ions, etc.) and is defined as the amount of substance containing exactly \$6.022 \times 10^{23}$ entities, which is Avogadro's number.
4. Note that the 'Avogadro constant' refers to the numerical value of the number of particles per mole, not the name of the quantity itself.
5. Conclude that the correct term for the number of carbon atoms in 12 grams of carbon-12 is a 'mole'.