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

• A. Subtract the atomic number from the mass number: neutrons = mass number - atomic number
• B. Add the atomic number and the mass number: neutrons = atomic number + mass number
• C. Divide the mass number by the atomic number: neutrons = mass number / atomic number
• D. Multiply the atomic number by the mass number: neutrons = atomic number × mass number

Answer: (A)

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 neutrons are the particles in the nucleus that have no charge, so the number of neutrons can be found by subtracting the number of protons from the total nucleons (protons + neutrons).
3. Write the relationship as an equation: \(\text{neutrons} = \text{mass number} - \text{atomic number}\) or \(n = A - Z\).
4. Evaluate the other options: Adding, dividing, or multiplying the atomic number and mass number do not correctly represent the number of neutrons because they do not reflect the difference between total nucleons and protons.
5. Conclude that the correct method to calculate the number of neutrons in an atom is to subtract the atomic number from the mass number.