Which statement best describes a mole in chemistry?

• A. A mole is the volume occupied by a gas at standard temperature and pressure.
• 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 carbon-12.
• D. A mole is the number of protons in one atom of hydrogen.

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 is not related to volume directly; volume depends on conditions like temperature and pressure, so the first statement about volume is incorrect.
4. Note that the mole is not a mass itself, although the mass of one mole of a substance (molar mass) is related to the atomic or molecular mass; thus, the statement about the mass of one atom of carbon-12 is incorrect.
5. Understand that the mole is not related to the number of protons in an atom, so the statement about the number of protons in hydrogen is incorrect.