Avogadro's number defines...

• A. Liters per mole
• B. Seconds per mole
• C. Particles per mole
• D. Moles per particle

Answer: (C)

Avogadro's number defines the conversion between amount of substance and the number of discrete particles. It tells you how many individual particles are in one mole of a substance, so the quantity of particles equals the number of moles times 6.022 × 10^23. This is why it’s described as particles per mole. The other ideas don’t fit because liters per mole would relate to volume per amount (not a fixed particle count), seconds per mole isn’t a meaningful unit in this context, and moles per particle is the reciprocal of Avogadro’s number, not the definition. For example, 2.0 moles contain about 1.2044 × 10^24 particles.