Which of the following pair(s) represent(s) the isoelectronic species ?

Options

A. `S^(2-)` & `Sc^(3+)`
B. `SO_(2)` & `NO_3^(-)`
C. `N_(2)` & `CN^(-)`
D. `NH_3` & `H_3O^+`

Explanation

To determine which pairs represent isoelectronic species, we need to find species that have the same number of electrons. Let's analyze each option step by step.

### Step 1: Understand Isoelectronic Species
Isoelectronic species are atoms, ions, or molecules that have the same number of electrons.

### Step 2: Analyze Each Pair
We will evaluate each pair given in the options.

#### Pair 1: S²⁻ and Sc³⁺
- **S²⁻ (Sulfur ion)**:
- Sulfur (S) has 16 electrons.
- The 2- charge means it has gained 2 electrons.
- Total electrons = 16 + 2 = 18 electrons.

- **Sc³⁺ (Scandium ion)**:
- Scandium (Sc) has 21 electrons.
- The 3+ charge means it has lost 3 electrons.
- Total electrons = 21 - 3 = 18 electrons.

**Conclusion**: S²⁻ and Sc³⁺ are isoelectronic (both have 18 electrons).

#### Pair 2: SO₂ and NO₃⁻
- **SO₂ (Sulfur dioxide)**:
- Sulfur has 16 electrons, and each oxygen has 8 electrons.
- Total electrons = 16 + 2 × 8 = 16 + 16 = 32 electrons.

- **NO₃⁻ (Nitrate ion)**:
- Nitrogen has 7 electrons, and each oxygen has 8 electrons.
- The 1- charge means it has gained 1 electron.
- Total electrons = 7 + 3 × 8 + 1 = 7 + 24 + 1 = 32 electrons.

**Conclusion**: SO₂ and NO₃⁻ are isoelectronic (both have 32 electrons).

#### Pair 3: CN⁻ and N₂
- **CN⁻ (Cyanide ion)**:
- Carbon has 6 electrons, and nitrogen has 7 electrons.
- The 1- charge means it has gained 1 electron.
- Total electrons = 6 + 7 + 1 = 14 electrons.

- **N₂ (Dinitrogen)**:
- Each nitrogen has 7 electrons.
- Total electrons = 2 × 7 = 14 electrons.

**Conclusion**: CN⁻ and N₂ are isoelectronic (both have 14 electrons).

#### Pair 4: NH₃ and H₃O⁺
- **NH₃ (Ammonia)**:
- Nitrogen has 7 electrons, and each hydrogen has 1 electron.
- Total electrons = 7 + 3 × 1 = 7 + 3 = 10 electrons.

- **H₃O⁺ (Hydronium ion)**:
- Oxygen has 8 electrons, and each hydrogen has 1 electron.
- The 1+ charge means it has lost 1 electron.
- Total electrons = 8 + 3 × 1 - 1 = 8 + 3 - 1 = 10 electrons.

**Conclusion**: NH₃ and H₃O⁺ are isoelectronic (both have 10 electrons).

### Final Conclusion
All pairs are isoelectronic:
1. S²⁻ and Sc³⁺ (18 electrons)
2. SO₂ and NO₃⁻ (32 electrons)
3. CN⁻ and N₂ (14 electrons)
4. NH₃ and H₃O⁺ (10 electrons)