Which of the following is closest to the atomic mass of magnesium (Mg)?

• A. 24.3 u
• B. 40.1 u
• C. 12.0 u
• D. 16.0 u

Answer: (A)

Verified step by step guidance

1. Understand that the atomic mass of an element is the weighted average mass of all its naturally occurring isotopes, measured in atomic mass units (u).
2. Recall that magnesium (Mg) is an element with atomic number 12, meaning it has 12 protons, and its atomic mass is close to the sum of protons and neutrons in its most common isotopes.
3. Look at the given options and recognize that 12.0 u corresponds roughly to the atomic mass of carbon, 16.0 u corresponds roughly to oxygen, and 40.1 u corresponds roughly to calcium.
4. Since magnesium has 12 protons and typically about 12 neutrons, its atomic mass should be close to 24 u, which matches the option 24.3 u.
5. Therefore, the atomic mass closest to magnesium is 24.3 u, based on its position in the periodic table and typical isotope composition.