`K^(+)` and `Cl^(-)` ions are isoelectronic.Which of the statement is not correct?

Options

A. Both `K^(+)` and `Cl^(-)` ions contains 18 electrons
B. Both `K^(+)` and `Cl^(-)` ions have same configuration.
C. `K^(+)` ions is bigger than `Cl^(-)` ion in ionic size.
D. `Cl^(-)` ions is bigger than `K^(+)` ion in size.

Explanation

To solve the question regarding the isoelectronic ions \( K^{+} \) and \( Cl^{-} \), we need to analyze their properties and determine which statement about them is not correct.

### Step-by-step Solution:

1. **Understanding Isoelectronic Species**:
- Isoelectronic species are atoms or ions that have the same number of electrons.
- In this case, both \( K^{+} \) and \( Cl^{-} \) have the same electron configuration: \( 1s^2, 2s^2, 2p^6, 3s^2, 3p^6 \), which corresponds to 18 electrons.

**Hint**: Recall that isoelectronic species have the same number of electrons, which affects their properties.

2. **Electronic Configuration**:
- The electronic configuration of potassium (\( K \)) is \( 1s^2, 2s^2, 2p^6, 3s^2, 3p^6, 4s^1 \).
- When potassium loses one electron to form \( K^{+} \), it loses the \( 4s \) electron, resulting in \( 1s^2, 2s^2, 2p^6, 3s^2, 3p^6 \).
- The electronic configuration of chlorine (\( Cl \)) is \( 1s^2, 2s^2, 2p^6, 3s^2, 3p^5 \).
- When chlorine gains one electron to form \( Cl^{-} \), it gains an electron in the \( 3p \) subshell, resulting in the same configuration as \( K^{+} \).

**Hint**: Write down the electronic configurations to visualize the changes when ions are formed.

3. **Comparing Ionic Sizes**:
- Cations (like \( K^{+} \)) are smaller than their parent atoms because they lose an electron, resulting in a stronger attraction between the nucleus and the remaining electrons.
- Anions (like \( Cl^{-} \)) are larger than their parent atoms because they gain an electron, which increases electron-electron repulsion in the outer shell, leading to a larger size.

**Hint**: Remember that cations are smaller than their neutral atoms, while anions are larger.

4. **Determining the Incorrect Statement**:
- The statements to evaluate are:
1. Both potassium and chlorine ions contain 18 electrons. (True)
2. Both potassium and chlorine ions have the same configuration. (True)
3. Potassium ion is bigger than chloride ion in ionic size. (False)
4. Chloride ion is bigger than potassium ion in ionic size. (True)

- The incorrect statement is option 3, which claims that the potassium ion is bigger than the chloride ion. This is not true; in fact, the chloride ion is larger than the potassium ion.

**Hint**: Compare the ionic sizes based on their charges and electron configurations.

### Final Answer:
The statement that is not correct is: **"Potassium ion is bigger than chloride ion in ionic size."**