Which of the following are isoelectronic?
`1K^(+)" "2. Ar" "3. Cl^(-)" "4. Ca^(+)`

Options

A. 2 and 3
B. 3 and 4
C. 2 and 4
D. All of these

Explanation

To determine which of the given species are isoelectronic, we need to find the number of electrons in each species. Isoelectronic species are those that have the same number of electrons.

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

2. **Argon (Ar)**:
- Atomic number of Ar = 18
- Ar is a neutral atom, so it has 18 electrons.
- Number of electrons in Ar = 18

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

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

Now, let's summarize the number of electrons in each species:
- K⁺: 18 electrons
- Ar: 18 electrons
- Cl⁻: 18 electrons
- Ca²⁺: 18 electrons

Since all four species have the same number of electrons (18), they are all isoelectronic.

**Final Answer**: All of the given species (K⁺, Ar, Cl⁻, Ca²⁺) are isoelectronic.