Which of the following correctly describes how to determine the number of neutrons in an atom?

• A. Add the atomic number to the mass number.
• B. Subtract the atomic number from the mass number.
• C. Divide the mass number by the atomic number.
• D. Multiply the atomic number by the mass number.

Answer: (B)

Verified step by step guidance

1. Understand the definitions: The atomic number (Z) represents the number of protons in an atom, and the mass number (A) represents the total number of protons and neutrons in the atom's nucleus.
2. Recall that the number of neutrons (N) can be found by subtracting the number of protons from the total nucleons, so the relationship is \(N = A - Z\).
3. Identify that adding the atomic number to the mass number would incorrectly increase the total count beyond the actual number of nucleons.
4. Recognize that dividing or multiplying the atomic number and mass number does not correspond to the physical meaning of neutrons in the nucleus.
5. Conclude that the correct method to find the number of neutrons is to subtract the atomic number from the mass number, i.e., \(N = A - Z\).