The mass number of a nucleus is equal to

Options

A. the number of neutrons in the nucleus
B. the number of protons in the nucleus
C. the number of nucleons in the nucleus
D. none of them

Answer

To solve the question regarding the mass number of a nucleus, we can break it down into the following steps:

### Step-by-Step Solution:

1. **Understand the Definition of Mass Number**:
The mass number (denoted as A) of a nucleus is defined as the total number of protons and neutrons present in that nucleus.

2. **Identify Protons and Neutrons**:
- Protons are positively charged particles found in the nucleus.
- Neutrons are neutral particles also located in the nucleus.
- Together, protons and neutrons are referred to as nucleons.

3. **Mathematical Representation**:
The mass number can be mathematically represented as:
\[ A = Z + N \]
where:
- \( A \) = mass number
- \( Z \) = number of protons
- \( N \) = number of neutrons

4. **Conclusion**:
Therefore, the mass number of a nucleus is equal to the sum of the number of protons and neutrons. It can also be stated that the mass number represents the total number of nucleons in the nucleus.

5. **Select the Correct Option**:
Based on the understanding that mass number is the sum of protons and neutrons, we can conclude that the correct option from the given choices is the one that states that the mass number is equal to the sum of the number of protons and neutrons.

### Final Answer:
The mass number of a nucleus is equal to the sum of the number of protons and neutrons.

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