Which one of the following sets of ions represents the collection of isoelectronic species?
(Atomic numbers : F = 9, CI = 17, Na = 11, Mg = 12,Al = 13, K = 19, Ca = 20, Sc =21)

Options

A. `K^(+) ,Ca^(2+) ,Sc^(3+) ,Cl^(-)`
B. `Na^(+) ,Ca^(2+) ,Sc^(3+) ,F^(-)`
C. `K^(+) ,Cl^(-) ,Mg^(2+) ,Sc^(3+)`
D. `Na^(+) , Mg^(2+) ,Al^(3+) ,Cl^(-)`

Explanation

To determine which set of ions represents isoelectronic species, we need to find the total number of electrons in each ion given their atomic numbers and charges. Isoelectronic species are ions or molecules that have the same number of electrons.

### Step-by-Step Solution:

1. **Identify the atomic numbers and charges of the ions:**
- K⁺ (Potassium): Atomic number = 19
- Ca²⁺ (Calcium): Atomic number = 20
- Sc³⁺ (Scandium): Atomic number = 21
- Cl⁻ (Chlorine): Atomic number = 17

2. **Calculate the number of electrons for each ion:**
- For K⁺:
- Atomic number = 19 (number of protons)
- Charge = +1 (lost 1 electron)
- Number of electrons = 19 - 1 = **18 electrons**

- For Ca²⁺:
- Atomic number = 20 (number of protons)
- Charge = +2 (lost 2 electrons)
- Number of electrons = 20 - 2 = **18 electrons**

- For Sc³⁺:
- Atomic number = 21 (number of protons)
- Charge = +3 (lost 3 electrons)
- Number of electrons = 21 - 3 = **18 electrons**

- For Cl⁻:
- Atomic number = 17 (number of protons)
- Charge = -1 (gained 1 electron)
- Number of electrons = 17 + 1 = **18 electrons**

3. **Compare the number of electrons:**
- K⁺ = 18 electrons
- Ca²⁺ = 18 electrons
- Sc³⁺ = 18 electrons
- Cl⁻ = 18 electrons

4. **Conclusion:**
- All the ions (K⁺, Ca²⁺, Sc³⁺, and Cl⁻) have the same number of electrons, which is 18. Therefore, they are isoelectronic species.

### Final Answer:
The set of ions K⁺, Ca²⁺, Sc³⁺, and Cl⁻ represents the collection of isoelectronic species.

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