What is atomic mass unit (amu)?

Explanation

**Step-by-Step Solution:**

1. **Definition of Atomic Mass Unit (amu)**:
- The atomic mass unit (amu) is a standard unit of mass that is used to express the masses of atoms and molecules.

2. **Purpose of AMU**:
- AMU is primarily used to compare the relative masses of different isotopes of elements. Isotopes are variants of a particular chemical element that have the same number of protons but different numbers of neutrons.

...