Which pair is of isoelectronic species?

Options

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

Explanation

To determine which pair consists of isoelectronic species, we need to identify species that have the same number of electrons. Here’s the step-by-step solution:

### Step 1: Identify the atomic numbers and electron configurations of the given species.

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

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

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

### Step 2: Compare the number of electrons in each species.

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

### Step 3: Check for isoelectronic pairs.

From the comparison:
- K+ and Cl- both have 18 electrons, making them isoelectronic.
- Na+ has only 10 electrons, so it is not isoelectronic with K+ or Cl-.

### Step 4: Check the second option with Ca²+ (Calcium ion).

1. **Ca²+**:
- Atomic number of Ca = 20
- Ca²+ loses 2 electrons: 20 - 2 = 18 electrons.

Now we have:
- K+ has 18 electrons.
- Cl- has 18 electrons.
- Ca²+ has 18 electrons.

### Conclusion:

K+, Cl-, and Ca²+ are isoelectronic species since they all have 18 electrons.

### Final Answer:

The pair of isoelectronic species is K+, Cl-, and Ca²+.

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