The mass number of an atom is determined by

• GC Atomic Structure

The mass number of an atom is determined by

1. the number of protons only
2. adding the number of neutrons and number of electrons
3. adding the number of protons and number of electrons
4. adding the number of neutrons and number of protons

Answer

Atomic mass number = Number of protons  + Number of neutrons

The correct option is D.