How do you work out the number of neutrons?

How do you work out the number of neutrons?

• A. Atomic number minus Mass number
• B. Mass number minus Atomic number
• C. Protons minus Neutrons
• D. Electrons minus Protons

Answer: (B)

Neutrons are found by subtracting the number of protons from the total number of particles in the nucleus. The mass number counts protons plus neutrons, while the atomic number counts only protons. So neutrons = mass number − atomic number. For example, carbon-12 has mass number 12 and atomic number 6, so it has 12 − 6 = 6 neutrons. This remains true even if the atom has gained or lost electrons (ionized), because ionization changes electrons, not the nucleus. The other ideas mix up what’s being counted or ignore the relationship between mass number, atomic number, and neutrons.

Neutrons are found by subtracting the number of protons from the total number of particles in the nucleus. The mass number counts protons plus neutrons, while the atomic number counts only protons. So neutrons = mass number − atomic number. For example, carbon-12 has mass number 12 and atomic number 6, so it has 12 − 6 = 6 neutrons. This remains true even if the atom has gained or lost electrons (ionized), because ionization changes electrons, not the nucleus. The other ideas mix up what’s being counted or ignore the relationship between mass number, atomic number, and neutrons.