The modern atomic mass unit if based on the mass of ………

Explanation

To answer the question regarding the modern atomic mass unit (AMU), we can break down the solution into the following steps:

### Step-by-Step Solution:

1. **Understanding Atomic Mass Unit (AMU)**:
- The atomic mass unit (AMU) is a unit of mass that is used to express atomic and molecular weights.

2. **Definition of 1 AMU**:
- One atomic mass unit (1 AMU) is defined as 1/12 of the mass of a carbon-12 atom.

3. **Mass of Carbon-12**:
- Carbon-12 is a stable isotope of carbon that has 6 protons and 6 neutrons. Its atomic mass is taken as the standard for measuring atomic masses.

4. **Relative Masses**:
- The masses of all other atoms are determined relative to the mass of the carbon-12 atom. This means that the atomic mass of any element is compared to the mass of carbon-12.

5. **Conclusion**:
- Therefore, the modern atomic mass unit is based on the mass of **one atom of carbon-12**.

### Final Answer:
The modern atomic mass unit is based on the mass of **one atom of carbon-12**.

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