What does Avogadro's number specify?

• A. The number of grams in one mole
• B. The number of particles in one mole
• C. The number of liters per mole
• D. The number of electrons in an atom

Answer: (B)

Avogadro's number is a counting constant that tells how many discrete entities are in one mole of any substance. One mole contains 6.022×10^23 particles, whether they are atoms, molecules, or ions. This number is the bridge between the macroscopic world (mass in grams, volume in liters) and the microscopic world (individual particles). For example, one mole of water has 6.022×10^23 water molecules and a mass of about 18.015 grams. The key idea is that Avogadro's number specifies the quantity of particles per mole, not a mass, a volume, or a fixed number of electrons.