Isoelectronic species are

Options

A. `N^(3-),O^(2-)`
B. `Na^(+),Ca^(2+)`
C. `O^(2-),P^(3-)`
D. `K^(+),Na^(+)`.

Answer

To determine which species are isoelectronic, we need to identify the number of electrons in each species provided in the options. Isoelectronic species are defined as species that have the same number of electrons.

### Step-by-Step Solution:

1. **Identify the first pair: N³⁻ and O²⁻**
- **N³⁻ (Nitride ion)**:
- Atomic number of nitrogen (N) = 7
- Electrons in neutral nitrogen = 7
- Gained 3 electrons = 7 + 3 = 10 electrons.
- **O²⁻ (Oxide ion)**:
- Atomic number of oxygen (O) = 8
- Electrons in neutral oxygen = 8
- Gained 2 electrons = 8 + 2 = 10 electrons.
- **Conclusion**: Both N³⁻ and O²⁻ have 10 electrons. Thus, they are isoelectronic.

2. **Identify the second pair: Na⁺ and Ca²⁺**
- **Na⁺ (Sodium ion)**:
- Atomic number of sodium (Na) = 11
- Electrons in neutral sodium = 11
- Lost 1 electron = 11 - 1 = 10 electrons.
- **Ca²⁺ (Calcium ion)**:
- Atomic number of calcium (Ca) = 20
- Electrons in neutral calcium = 20
- Lost 2 electrons = 20 - 2 = 18 electrons.
- **Conclusion**: Na⁺ has 10 electrons, while Ca²⁺ has 18 electrons. They are not isoelectronic.

3. **Identify the third pair: O²⁻ and P³⁻**
- **O²⁻ (Oxide ion)**:
- As calculated earlier, O²⁻ has 10 electrons.
- **P³⁻ (Phosphide ion)**:
- Atomic number of phosphorus (P) = 15
- Electrons in neutral phosphorus = 15
- Gained 3 electrons = 15 + 3 = 18 electrons.
- **Conclusion**: O²⁻ has 10 electrons, while P³⁻ has 18 electrons. They are not isoelectronic.

4. **Identify the fourth pair: K⁺ and Na⁺**
- **K⁺ (Potassium ion)**:
- Atomic number of potassium (K) = 19
- Electrons in neutral potassium = 19
- Lost 1 electron = 19 - 1 = 18 electrons.
- **Na⁺ (Sodium ion)**:
- As calculated earlier, Na⁺ has 10 electrons.
- **Conclusion**: K⁺ has 18 electrons, while Na⁺ has 10 electrons. They are not isoelectronic.

### Final Conclusion:
The only pair of isoelectronic species from the options provided is **N³⁻ and O²⁻**.

### Answer:
1. N³⁻ and O²⁻ are isoelectronic species.