**Question: What is the atomic mass unit (AMU)?**

- A unit of mass equal to 1/12 the mass of a carbon-12 atom
- A unit of mass equal to the mass of a proton
- A unit of mass equal to the mass of a neutron
- A unit of mass equal to the mass of an electron

**Answer:** (A)

**Solution:**

The atomic mass unit (AMU), also known as the Dalton, is a unit of mass equal to 1/12 the mass of a carbon-12 atom. The carbon-12 atom is the most abundant isotope of carbon, and it is used as the standard for measuring atomic masses. One AMU is equal to 1.660538921 × 10⁻²⁴ grams.

**Significance:**

- The use of atomic mass units provides a convenient way to compare the relative masses of different atoms and molecules. It simplifies calculations and allows chemists to work with manageable numbers.

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