What is the mass number of an atom that contains 5 protons and 7 neutrons?

• A. 7
• B. 35
• C. 5
• D. 12

Answer: (D)

Verified step by step guidance

1. Identify the number of protons in the atom, which is given as 5. The number of protons defines the atomic number.
2. Identify the number of neutrons in the atom, which is given as 7.
3. Recall that the mass number of an atom is the sum of the number of protons and neutrons: \(\text{Mass Number} = \text{Number of Protons} + \text{Number of Neutrons}\).
4. Substitute the given values into the formula: \(\text{Mass Number} = 5 + 7\).
5. Add the values to find the mass number, which represents the total number of nucleons in the atom.