Calcium has an atomic number of 20 and an atomic mass of 40. Therefore, a neutral calcium atom must have:

• A. 40 protons, 20 neutrons, and 20 electrons
• B. 20 protons, 20 neutrons, and 40 electrons
• C. 20 protons, 20 neutrons, and 20 electrons
• D. 20 protons, 40 neutrons, and 20 electrons

Answer: (C)

Verified step by step guidance

1. Identify the atomic number of calcium, which is 20. The atomic number represents the number of protons in the atom.
2. Recognize that a neutral atom has an equal number of protons and electrons. Therefore, the number of electrons in a neutral calcium atom is also 20.
3. Use the atomic mass (given as 40) to find the number of neutrons. The atomic mass is approximately the sum of protons and neutrons: \(\text{Atomic Mass} = \text{Protons} + \text{Neutrons}\).
4. Rearrange the formula to solve for neutrons: \(\text{Neutrons} = \text{Atomic Mass} - \text{Protons}\).
5. Substitute the known values: \(\text{Neutrons} = 40 - 20\), which gives the number of neutrons in the calcium atom.