The electronic configuration of an ion `Z^2-` is 2, 8. If the number of neutrons present in the parent atom Z is 11 then the nucleon no. of 'Z' is

Options

A. 16
B. 19
C. 20
D. 21

Answer

To find the nucleon number of the atom \( Z \) given the ion \( Z^{2-} \) and the number of neutrons, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Electronic Configuration of the Ion:**
The electronic configuration of the ion \( Z^{2-} \) is given as \( 2, 8 \). This indicates that the ion has a total of 10 electrons.

2. **Determine the Atomic Number of \( Z \):**
Since \( Z^{2-} \) has gained 2 electrons compared to the neutral atom \( Z \), we can find the atomic number of \( Z \) by subtracting 2 from the total number of electrons in the ion:
\[ \text{Atomic number of } Z = 10 - 2 = 8 \]

3. **Use the Number of Neutrons to Find the Nucleon Number:**
The nucleon number (mass number) is the sum of the number of protons (atomic number) and the number of neutrons. We know:
- Atomic number of \( Z \) = 8 (from step 2)
- Number of neutrons = 11 (given in the question)

Therefore, we can calculate the nucleon number as follows:
\[ \text{Nucleon number} = \text{Atomic number} + \text{Number of neutrons} = 8 + 11 = 19 \]

4. **Conclusion:**
The nucleon number of the atom \( Z \) is 19.

### Final Answer:
The nucleon number of \( Z \) is **19**.