The number of nucleons in an atom of atomic number Z and mass number A is

Options

A. zero
B. Z
C. A-Z
D. A

Answer

To determine the number of nucleons in an atom with atomic number \( Z \) and mass number \( A \), follow these steps:

### Step-by-Step Solution:

1. **Understand the Definitions**:
- The **atomic number** \( Z \) represents the number of protons in the nucleus of the atom.
- The **mass number** \( A \) represents the total number of nucleons in the nucleus, which includes both protons and neutrons.

2. **Identify the Components of Mass Number**:
- The mass number \( A \) can be expressed as:
\[ A = \text{Number of Protons} + \text{Number of Neutrons} \]
- Therefore, the number of protons is equal to \( Z \).

3. **Calculate the Number of Neutrons**:
- The number of neutrons can be calculated using the formula:
\[ \text{Number of Neutrons} = A - Z \]

4. **Determine the Total Number of Nucleons**:
- Since the total number of nucleons is the sum of protons and neutrons, we can write:
\[ \text{Total Nucleons} = Z + (A - Z) = A \]

5. **Conclusion**:
- Therefore, the number of nucleons in an atom with atomic number \( Z \) and mass number \( A \) is simply equal to \( A \).

### Final Answer:
The number of nucleons in an atom of atomic number \( Z \) and mass number \( A \) is \( A \).

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