Which statement best describes a mole in chemistry?

• A. A mole is the number of atoms in one gram of any element.
• B. A mole is the amount of substance that contains exactly 6.022 × 10^{23} elementary entities.
• C. A mole is the mass of one atom of hydrogen in grams.
• D. A mole is the volume occupied by one gram of a substance at standard temperature and pressure.

Answer: (B)

Verified step by step guidance

1. Understand that a mole is a fundamental concept in chemistry used to count particles such as atoms, molecules, or ions, similar to how a dozen counts 12 items.
2. Recall that the mole is defined by a specific number called Avogadro's number, which is exactly \$6.022 \times 10^{23}$ elementary entities (atoms, molecules, ions, etc.).
3. Recognize that the mole does not refer to mass directly, so statements about grams or mass of atoms are not accurate definitions of a mole.
4. Note that the mole is not related to volume directly, so volume-based definitions (like volume at standard temperature and pressure) do not describe a mole.
5. Conclude that the best description of a mole is the amount of substance containing exactly \$6.022 \times 10^{23}$ elementary entities, which is a fixed number used universally in chemistry.