In isoelectronic species `Cl^(-),Ar,Ca^(2+)` size differ due to

Options

A. Nuclear charge
B. Principal quantum number of valence shell
C. Azimuthal quantum number of valence shell
D. Electron-electron interaction in the outer orbitals

Explanation

To solve the question regarding the size differences in isoelectronic species \( \text{Cl}^-, \text{Ar}, \text{Ca}^{2+} \), we will analyze the factors affecting atomic size in these species.

### Step 1: Identify the Isoelectronic Species
The species given are:
- \( \text{Cl}^- \) (Chloride ion)
- \( \text{Ar} \) (Argon)
- \( \text{Ca}^{2+} \) (Calcium ion)

All three species have the same number of electrons, which is 18.

### Step 2: Determine the Number of Protons
Next, we need to consider the number of protons in each species:
- \( \text{Cl}^- \): Atomic number = 17 (17 protons)
- \( \text{Ar} \): Atomic number = 18 (18 protons)
- \( \text{Ca}^{2+} \): Atomic number = 20 (20 protons)

### Step 3: Understand the Concept of Nuclear Charge
The nuclear charge is the total charge of the nucleus, which is equal to the number of protons. As the number of protons increases, the nuclear charge increases. This increased nuclear charge results in a stronger attraction between the nucleus and the electrons.

### Step 4: Analyze the Effect on Atomic Size
- **For \( \text{Cl}^- \)**: 17 protons, weaker nuclear charge, larger size.
- **For \( \text{Ar} \)**: 18 protons, stronger nuclear charge than \( \text{Cl}^- \), smaller size than \( \text{Cl}^- \).
- **For \( \text{Ca}^{2+} \)**: 20 protons, strongest nuclear charge, smallest size among the three.

### Step 5: Conclusion on Size Order
The order of size from largest to smallest is:
\[ \text{Cl}^- > \text{Ar} > \text{Ca}^{2+} \]

### Final Answer
The size differences in the isoelectronic species \( \text{Cl}^-, \text{Ar}, \text{Ca}^{2+} \) are due to **nuclear charge**.

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