To determine the average number of neutrons, which operation is used?

To determine the average number of neutrons, which operation is used?

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

Answer: (A)

Neutrons come from the difference between the mass number and the atomic number. The mass number is the total count of protons and neutrons, while the atomic number is the count of protons. So the number of neutrons = mass number − atomic number. This is why subtracting the atomic number from the mass number gives the neutron count. For example, a nucleus with mass number 23 and atomic number 11 has 23 − 11 = 12 neutrons. If you were averaging neutrons across isotopes, you’d apply this same subtraction to each isotope and then average those results.

Neutrons come from the difference between the mass number and the atomic number. The mass number is the total count of protons and neutrons, while the atomic number is the count of protons. So the number of neutrons = mass number − atomic number. This is why subtracting the atomic number from the mass number gives the neutron count. For example, a nucleus with mass number 23 and atomic number 11 has 23 − 11 = 12 neutrons. If you were averaging neutrons across isotopes, you’d apply this same subtraction to each isotope and then average those results.