Which one of the following groups represent a collection of isolectronic species ? (At.no `Cs = 55, Br = 35)`

Options

A. `Na^(+),Ca^(2+),Mg^(2+)`
B. `N^(3-),F^(-),Na^(+)`
C. `Be,Al^(3+),Cl^(-)`
D. `Ca^(2+),Cs^(+),Br`

Answer

To determine which group represents a collection of isoelectronic species, we need to identify species that have the same number of electrons. Let's analyze the options step-by-step.

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

### Step 2: Analyze Each Option
We will evaluate each option provided in the question to check if they are isoelectronic.

#### Option A: Sodium ion (Na⁺), Calcium ion (Ca²⁺), Magnesium ion (Mg²⁺)
- **Sodium ion (Na⁺)**: Atomic number = 11, loses 1 electron → 11 - 1 = 10 electrons.
- **Calcium ion (Ca²⁺)**: Atomic number = 20, loses 2 electrons → 20 - 2 = 18 electrons.
- **Magnesium ion (Mg²⁺)**: Atomic number = 12, loses 2 electrons → 12 - 2 = 10 electrons.

**Conclusion for Option A**: Na⁺ has 10 electrons, Ca²⁺ has 18 electrons, and Mg²⁺ has 10 electrons. Not all have the same number of electrons. **Not isoelectronic.**

#### Option B: Nitride (N³⁻), Fluoride (F⁻), Sodium ion (Na⁺)
- **Nitride (N³⁻)**: Atomic number = 7, gains 3 electrons → 7 + 3 = 10 electrons.
- **Fluoride (F⁻)**: Atomic number = 9, gains 1 electron → 9 + 1 = 10 electrons.
- **Sodium ion (Na⁺)**: Atomic number = 11, loses 1 electron → 11 - 1 = 10 electrons.

**Conclusion for Option B**: All three species (N³⁻, F⁻, Na⁺) have 10 electrons. **They are isoelectronic.**

#### Option C: Beryllium (Be), Aluminium ion (Al³⁺), Chloride ion (Cl⁻)
- **Beryllium (Be)**: Atomic number = 4 → 4 electrons.
- **Aluminium ion (Al³⁺)**: Atomic number = 13, loses 3 electrons → 13 - 3 = 10 electrons.
- **Chloride ion (Cl⁻)**: Atomic number = 17, gains 1 electron → 17 + 1 = 18 electrons.

**Conclusion for Option C**: Be has 4 electrons, Al³⁺ has 10 electrons, and Cl⁻ has 18 electrons. **Not isoelectronic.**

#### Option D: Calcium ion (Ca²⁺), Cesium ion (Cs⁺), Bromine (Br)
- **Calcium ion (Ca²⁺)**: Already established → 18 electrons.
- **Cesium ion (Cs⁺)**: Atomic number = 55, loses 1 electron → 55 - 1 = 54 electrons.
- **Bromine (Br)**: Atomic number = 35 → 35 electrons.

**Conclusion for Option D**: Ca²⁺ has 18 electrons, Cs⁺ has 54 electrons, and Br has 35 electrons. **Not isoelectronic.**

### Final Conclusion
The only option that contains isoelectronic species is **Option B: Nitride (N³⁻), Fluoride (F⁻), Sodium ion (Na⁺)**, as all have 10 electrons.