Which of the following halides is most acidic ?

Options

A. `F^(-)`
B. `Br^(-)`
C. `I^(-)`
D. `Cl^(-)`

Explanation

To determine which halide is the most acidic, we can follow these steps:

### Step 1: Identify the Acids
First, we need to identify the acids corresponding to the halides in question. The halides we consider are fluoride (F), chloride (Cl), bromide (Br), and iodide (I). The acids formed from these halides are:
- HF (hydrofluoric acid)
- HCl (hydrochloric acid)
- HBr (hydrobromic acid)
- HI (hydroiodic acid)

### Step 2: Analyze Acid Strength
To determine the acidity, we need to analyze the stability of the conjugate bases formed after the acids donate a proton (H⁺). The conjugate bases are:
- F⁻ (from HF)
- Cl⁻ (from HCl)
- Br⁻ (from HBr)
- I⁻ (from HI)

### Step 3: Compare Stability of Conjugate Bases
The acidity of an acid is related to the stability of its conjugate base. A more stable conjugate base corresponds to a stronger acid. We will compare the stability of the conjugate bases F⁻, Cl⁻, Br⁻, and I⁻.

1. **Electronegativity**: Along the period, the more electronegative atom with a negative charge is more stable. However, in this case, we are comparing the stability of anions down the group.

2. **Size Factor**: Down the group, the size of the halide ions increases. As the size increases, the charge density decreases, leading to greater stability of the anion.

### Step 4: Order of Stability
The order of stability of the conjugate bases is as follows:
- I⁻ (largest size, most stable)
- Br⁻
- Cl⁻
- F⁻ (smallest size, least stable)

### Step 5: Conclusion on Acidity
Since the stability of the conjugate base directly correlates with the strength of the acid, we can conclude that:
- HI is the strongest acid because I⁻ is the most stable conjugate base.

### Final Answer
Thus, the most acidic halide is **HI**.

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