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

Options

A. `N^(3–) , O^(2–) , F^(–) , S^(2–)`
B. `Li^(+), Na^(+), Mg^(2+), Ca^(2+)`
C. `Ba^(2+), Sr^(2+), K^(+), Ca^(2+)`
D. `K^(+) , Cl^(–) , Ca^(2+), Sc^(3+)`

Answer

To determine which set of ions represents a collection of isoelectronic species, we need to find ions that have the same number of electrons.

### Step-by-Step Solution:

1. **Identify the number of electrons in each species:**
- **Fluorine (F)**: Atomic number = 9, so F has 9 electrons.
- **Chlorine (Cl)**: Atomic number = 17, so Cl has 17 electrons.
- **Sodium (Na)**: Atomic number = 11, so Na has 11 electrons.
- **Magnesium (Mg)**: Atomic number = 12, so Mg has 12 electrons.
- **Aluminium (Al)**: Atomic number = 13, so Al has 13 electrons.
- **Potassium (K)**: Atomic number = 19, so K has 19 electrons.
- **Calcium (Ca)**: Atomic number = 20, so Ca has 20 electrons.
- **Scandium (Sc)**: Atomic number = 21, so Sc has 21 electrons.

2. **Determine the electron count for the ions:**
- **F⁻**: 9 + 1 = 10 electrons (gains 1 electron)
- **Cl⁻**: 17 + 1 = 18 electrons (gains 1 electron)
- **Na⁺**: 11 - 1 = 10 electrons (loses 1 electron)
- **Mg²⁺**: 12 - 2 = 10 electrons (loses 2 electrons)
- **Al³⁺**: 13 - 3 = 10 electrons (loses 3 electrons)
- **K⁺**: 19 - 1 = 18 electrons (loses 1 electron)
- **Ca²⁺**: 20 - 2 = 18 electrons (loses 2 electrons)
- **Sc³⁺**: 21 - 3 = 18 electrons (loses 3 electrons)

3. **Group the ions by their electron counts:**
- **10 electrons**: F⁻, Na⁺, Mg²⁺, Al³⁺
- **18 electrons**: Cl⁻, K⁺, Ca²⁺, Sc³⁺

4. **Identify the isoelectronic sets:**
- The first group (F⁻, Na⁺, Mg²⁺, Al³⁺) has 10 electrons.
- The second group (Cl⁻, K⁺, Ca²⁺, Sc³⁺) has 18 electrons.

5. **Conclusion:**
- The set of ions that are isoelectronic is **F⁻, Na⁺, Mg²⁺, Al³⁺** (10 electrons).
- Alternatively, **Cl⁻, K⁺, Ca²⁺, Sc³⁺** also represents a set of isoelectronic species (18 electrons).

### Final Answer:
The ions that represent a collection of isoelectronic species are **F⁻, Na⁺, Mg²⁺, Al³⁺** (10 electrons) or **Cl⁻, K⁺, Ca²⁺, Sc³⁺** (18 electrons).