HI cannot be prepared by the action of conc. `H_(2)SO_(4)` on KI because

Options

A. HI is stronger acid than `H_(2)SO_(4)`
B. `H_(2)SO_(4)` is stronger oxidising agent than HI
C. `H_(2)SO_(4)` is an oxidising agent
D. HI is strong reducing agent

Answer

To understand why HI cannot be prepared by the action of concentrated H₂SO₄ on KI, we need to analyze the properties of the substances involved and the reactions that take place. Here’s a step-by-step breakdown of the reasoning:

### Step 1: Identify the Reactants
The reactants in this scenario are concentrated sulfuric acid (H₂SO₄) and potassium iodide (KI).

### Step 2: Understand the Nature of H₂SO₄
Concentrated sulfuric acid is a strong acid and also a strong oxidizing agent. This means it has the ability to oxidize other substances while itself being reduced.

### Step 3: Understand the Nature of HI
Hydroiodic acid (HI) is a strong acid and also acts as a strong reducing agent. This means it can donate electrons to other substances, reducing them while itself being oxidized.

### Step 4: Analyze the Reaction
When KI is treated with concentrated H₂SO₄, the expected reaction would be:
\[ \text{KI} + \text{H}_2\text{SO}_4 \rightarrow \text{KHSO}_4 + \text{HI} \]

However, if HI is formed, it can further react with H₂SO₄:
\[ 2 \text{HI} + \text{H}_2\text{SO}_4 \rightarrow \text{SO}_2 + \text{I}_2 + 2 \text{H}_2\text{O} \]

### Step 5: Determine the Outcome
In this reaction, HI acts as a reducing agent and reduces sulfuric acid to sulfur dioxide (SO₂), while itself being oxidized to iodine (I₂). This means that once HI is formed, it will not remain in the solution because it will react with H₂SO₄.

### Conclusion
Due to the oxidizing nature of H₂SO₄ and the reducing nature of HI, the formation of HI is not feasible when concentrated H₂SO₄ is used. Instead, HI will be oxidized to I₂, preventing its preparation.

### Final Answer
HI cannot be prepared by the action of concentrated H₂SO₄ on KI because H₂SO₄ is a strong oxidizing agent and HI is a strong reducing agent. The HI formed would be oxidized to iodine, hence it cannot be isolated.

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