ANSWER:
The correct option is D: Atomic Mass Unit. Atomic mass is the "mass of an atom" of elements which is measured in amu or atomic mass unit.
EXPLANATION:
- The atomic mass is found to be equivalent to the "number of protons and neutrons" in an atom which is also the "mass number" of an atom.
- The atomic mass is known as atomic weight which is equal to the "weighted average" of "isotopes" of an element.
