Atomic number of a metal having 12 neutrons and mass number 23 is __________ .

Explanation

To find the atomic number of a metal with 12 neutrons and a mass number of 23, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Definitions**:
- The **mass number (A)** of an atom is the sum of the number of protons (Z) and the number of neutrons (N) in its nucleus.
- The **atomic number (Z)** is the number of protons in the nucleus of an atom.

2. **Write the Formula for Mass Number**:
- The formula for mass number is:
\[ A = Z + N \]
- Where:
- \( A \) = mass number
- \( Z \) = atomic number (number of protons)
- \( N \) = number of neutrons

3. **Substitute the Known Values**:
- We are given:
- Mass number \( A = 23 \)
- Number of neutrons \( N = 12 \)
- Substitute these values into the formula:
\[ 23 = Z + 12 \]

4. **Solve for Atomic Number (Z)**:
- Rearranging the equation to find \( Z \):
\[ Z = 23 - 12 \]
- Calculate:
\[ Z = 11 \]

5. **Conclusion**:
- The atomic number of the metal is **11**.

### Final Answer:
The atomic number of the metal having 12 neutrons and a mass number of 23 is **11**.

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