Which pair out of these is isoelectronic

Options

A. `K^(+),CI^(-),Na^(+)`
B. `K^(+),CI^(-),Ca^(2+)`
C. `F^(-),AI^(+3),K^(+)`
D. `Fe^(+3),Cu^(+2),V^(+3)`

Answer

To determine which pair of the given species is isoelectronic, we need to follow these steps:

### Step 1: Understand Isoelectronic Species
Isoelectronic species are atoms or ions that have the same number of electrons. This means that they will have the same electronic configuration.

### Step 2: Identify the Atomic Numbers
We need to find the atomic numbers of the given species in the pairs. The atomic number tells us how many electrons are present in a neutral atom.

### Step 3: Calculate the Number of Electrons for Each Species
For each ion, we will adjust the number of electrons based on its charge:
- If the species is positively charged, it has lost electrons.
- If the species is negatively charged, it has gained electrons.

### Step 4: Compare the Number of Electrons
We will compare the number of electrons for each pair to see if they are the same.

### Step 5: Analyze the Given Pairs
Let’s analyze the pairs one by one.

1. **K⁺ (Potassium ion)**
- Atomic number of K = 19
- K⁺ has lost 1 electron: 19 - 1 = 18 electrons.

2. **Cl⁻ (Chloride ion)**
- Atomic number of Cl = 17
- Cl⁻ has gained 1 electron: 17 + 1 = 18 electrons.

3. **Ca²⁺ (Calcium ion)**
- Atomic number of Ca = 20
- Ca²⁺ has lost 2 electrons: 20 - 2 = 18 electrons.

From the calculations above, K⁺, Cl⁻, and Ca²⁺ all have 18 electrons, making them isoelectronic.

### Step 6: Check Other Pairs
Now, let's check the other pairs to confirm they are not isoelectronic.

1. **F⁻ and Al³⁺**
- F⁻: Atomic number = 9, 9 + 1 = 10 electrons.
- Al³⁺: Atomic number = 13, 13 - 3 = 10 electrons.
- Not isoelectronic with K⁺, Cl⁻, Ca²⁺.

2. **Fe³⁺ and Cu²⁺**
- Fe³⁺: Atomic number = 26, 26 - 3 = 23 electrons.
- Cu²⁺: Atomic number = 29, 29 - 2 = 27 electrons.
- Not isoelectronic.

3. **V³⁺**
- V: Atomic number = 23, 23 - 3 = 20 electrons.
- Not isoelectronic.

### Conclusion
The only pair that is isoelectronic is **K⁺, Cl⁻, and Ca²⁺**.

### Final Answer
The correct pair of isoelectronic species is K⁺, Cl⁻, and Ca²⁺.

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