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

• A. 16.0 u
• B. 32.1 u
• C. 12.0 u
• D. 24.3 u

Answer: (D)

Verified step by step guidance

1. Understand that the atomic mass of an element is the weighted average mass of all the isotopes of that element, measured in atomic mass units (u).
2. Identify the element in question, which is magnesium (Mg), and recall that its atomic number is 12, meaning it has 12 protons.
3. Recognize that the atomic mass is not simply the number of protons but includes the average mass of protons and neutrons in the nucleus, weighted by isotope abundance.
4. Recall or look up the approximate atomic mass of magnesium, which is around 24.3 u, reflecting the natural isotopic distribution of magnesium isotopes.
5. Compare the given options (16.0 u, 32.1 u, 12.0 u) to the known atomic mass of magnesium and identify which value is closest to 24.3 u.