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 ions is isoelectronic, we need to identify the number of electrons in each ion. Isoelectronic species have the same number of electrons. Let's analyze the options step by step.

### Step 1: Identify the number of electrons in each ion

1. **K⁺ (Potassium ion)**
- Atomic number of K = 19
- K loses 1 electron to become K⁺.
- Number of electrons in K⁺ = 19 - 1 = **18 electrons**.

2. **Cl⁻ (Chloride ion)**
- Atomic number of Cl = 17
- Cl gains 1 electron to become Cl⁻.
- Number of electrons in Cl⁻ = 17 + 1 = **18 electrons**.

3. **Na⁺ (Sodium ion)**
- Atomic number of Na = 11
- Na loses 1 electron to become Na⁺.
- Number of electrons in Na⁺ = 11 - 1 = **10 electrons**.

### Step 2: Compare the number of electrons

- K⁺ has **18 electrons**.
- Cl⁻ has **18 electrons**.
- Na⁺ has **10 electrons**.

From this, we can see that K⁺ and Cl⁻ are isoelectronic (both have 18 electrons), while Na⁺ is not.

### Step 3: Check the second option

1. **Ca²⁺ (Calcium ion)**
- Atomic number of Ca = 20
- Ca loses 2 electrons to become Ca²⁺.
- Number of electrons in Ca²⁺ = 20 - 2 = **18 electrons**.

Now we can summarize:

- K⁺: 18 electrons
- Cl⁻: 18 electrons
- Ca²⁺: 18 electrons

### Conclusion for the second option
K⁺, Cl⁻, and Ca²⁺ are all isoelectronic because they all have **18 electrons**.

### Step 4: Check the third option

1. **F⁻ (Fluoride ion)**
- Atomic number of F = 9
- F gains 1 electron to become F⁻.
- Number of electrons in F⁻ = 9 + 1 = **10 electrons**.

2. **Al³⁺ (Aluminum ion)**
- Atomic number of Al = 13
- Al loses 3 electrons to become Al³⁺.
- Number of electrons in Al³⁺ = 13 - 3 = **10 electrons**.

3. **K⁺ (Potassium ion)**
- As calculated earlier, K⁺ has **18 electrons**.

### Conclusion for the third option
F⁻ and Al³⁺ are isoelectronic (both have 10 electrons), but K⁺ is not isoelectronic with them.

### Step 5: Check the fourth option

1. **Fe³⁺ (Iron ion)**
- Atomic number of Fe = 26
- Fe loses 3 electrons to become Fe³⁺.
- Number of electrons in Fe³⁺ = 26 - 3 = **23 electrons**.

2. **Cu²⁺ (Copper ion)**
- Atomic number of Cu = 29
- Cu loses 2 electrons to become Cu²⁺.
- Number of electrons in Cu²⁺ = 29 - 2 = **27 electrons**.

3. **V³⁺ (Vanadium ion)**
- Atomic number of V = 23
- V loses 3 electrons to become V³⁺.
- Number of electrons in V³⁺ = 23 - 3 = **20 electrons**.

### Conclusion for the fourth option
Fe³⁺, Cu²⁺, and V³⁺ are not isoelectronic with each other as they have different numbers of electrons.

### Final Answer
The pair that is isoelectronic is **K⁺, Cl⁻, and Ca²⁺** (Option 2).

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