Chloride ion and potassium ion are isoelectronic, then

Options

A. their sizes are same
B. `Cl^-` ion is bigger than `K^-` ion
C. `K^+` ion is relatively begger
D. their sizes depend on other cation and anion

Answer

To solve the question regarding the sizes of the chloride ion (Cl⁻) and the potassium ion (K⁺), which are isoelectronic, we can follow these steps:

### 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 Cl⁻ and K⁺ have 18 electrons.

2. **Identifying the Ions**:
- The chloride ion (Cl⁻) is formed when chlorine gains one electron, resulting in a total of 17 protons and 18 electrons.
- The potassium ion (K⁺) is formed when potassium loses one electron, resulting in a total of 19 protons and 18 electrons.

3. **Comparing the Nuclei**:
- The size of an ion is influenced by the number of protons in the nucleus. The more protons present, the stronger the positive charge of the nucleus, which pulls the electrons closer.
- Cl⁻ has 17 protons, while K⁺ has 19 protons.

4. **Analyzing the Size**:
- Since K⁺ has more protons (19) than Cl⁻ (17), the effective nuclear charge experienced by the electrons in K⁺ is greater. This leads to a stronger attraction between the nucleus and the electrons in K⁺, resulting in a smaller ionic radius compared to Cl⁻.
- Conversely, Cl⁻, being an anion, has an increased electron-electron repulsion due to the additional electron, which makes it larger.

5. **Conclusion**:
- Therefore, since Cl⁻ is an anion and K⁺ is a cation, and considering the effective nuclear charge, we conclude that Cl⁻ is larger than K⁺.
- The final answer is: **Cl⁻ is larger than K⁺**.