The mass number of a nucleus is
- Athe sum of the numbers of neutrons and protons
- Bthe total mass of neutrons and protons
- Calways more than the atomic weight
- Dalways less than its atomic number
- ENone of the above/More than one of the above
Show answer and explanation
Correct answer: (a) the sum of the numbers of neutrons and protons
Explanation
Mass number (A) is the total number of protons and neutrons (nucleons) present in the nucleus.
Atomic number (Z) counts only protons; the number of neutrons is N = A – Z.
It is a whole number and differs from atomic weight, which is an averaged value over isotopes.