An atom contains 11 protons and 12 neutrons. What are its atomic number and mass number?

• A. Atomic number: 12; Mass number: 11
• B. Atomic number: 12; Mass number: 23
• C. Atomic number: 11; Mass number: 12
• D. Atomic number: 11; Mass number: 23

Answer: (D)

Verified step by step guidance

1. Identify the number of protons in the atom. The number of protons determines the atomic number. Here, the atom has 11 protons.
2. Recall that the atomic number (Z) is equal to the number of protons, so the atomic number is 11.
3. Determine the number of neutrons, which is given as 12 in this problem.
4. Calculate the mass number (A) by adding the number of protons and neutrons: \(A = \text{protons} + \text{neutrons} = 11 + 12\).
5. Conclude that the atomic number is 11 and the mass number is 23, matching the correct answer choice.