6.022 × 10^23 particles per mole

• A. Molar mass
• B. Avogadro's number
• C. Mole
• D. Atomic number

Answer: (B)

The concept here is the link between amount of substance and the number of particles. Avogadro's number, 6.022 × 10^23, is the exact number of particles in one mole of any substance. It serves as the bridge that lets us count microscopic entities by using the macroscopic unit of a mole, so one mole contains that many particles regardless of the substance.

This is why Avogadro's number is the best answer: it is the constant that directly defines how many particles correspond to a mole. Molar mass tells you how much mass per mole (in grams per mole), not how many particles are present. A mole is the amount of substance, a count of how many entities it contains, but the specific count per mole is given by Avogadro's number. The atomic number describes the number of protons in an atom and identifies the element, not the quantity of particles in a mole.