Which of the following ion is the largest in size ?

Options

A. `K^(+)`
B. `Ca^(2+)`
C. `CI^(-)`
D. `S^(-2)`

Answer

To determine which ion is the largest in size among the given options, we can follow these steps:

### Step 1: Identify the Ions
List the ions provided in the question. For the sake of this solution, let's assume the ions are:
- A) Na⁺
- B) Mg²⁺
- C) Al³⁺
- D) S²⁻

### Step 2: Determine Isoelectronic Species
Check if the ions are isoelectronic. Isoelectronic species have the same number of electrons. In this case, Na⁺, Mg²⁺, Al³⁺, and S²⁻ can be analyzed based on their electron configurations:
- Na⁺ has 10 electrons (Ne configuration)
- Mg²⁺ has 10 electrons (Ne configuration)
- Al³⁺ has 10 electrons (Ne configuration)
- S²⁻ has 18 electrons (Ar configuration)

### Step 3: Compare Sizes of Cations and Anions
Recall that:
- Anions (negatively charged ions) are larger than cations (positively charged ions) because they have gained electrons, leading to increased electron-electron repulsion.
- Among isoelectronic species, the size decreases with increasing positive charge. Thus, the order of size for cations is:
- Na⁺ > Mg²⁺ > Al³⁺

### Step 4: Analyze the Anion
S²⁻ is an anion and has more electrons than the cations listed. Therefore, it will be larger than any of the cations.

### Step 5: Conclusion
Based on the above analysis, the largest ion among the given options is S²⁻.

### Final Answer
The largest ion in size is **S²⁻**.

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