Sulphuric acid is considered as the king of chemicals. The prosperity of any country is measured by the amount of sulphuric acid it consumes. Sulphuric acid is, thus, a substance of very great commercial importance as it used practically ine every important industry. This is due to the following properties of sulphuric acid :
(a) acidic nature
(b) oxidising nature
(c) dehydrating nature
(d) sulphonation.
Concentrated `H_2 SO_4` cannot be used to prepare `HBr` or `HI` from `KBr` or `KI` because it.

Options

A. Reacts too slowly with `KBr` or `KI`.
B. Reducing `HBr` or `HI`
C. Oxidising `HBr` or `HI`
D. Oxidises `KBr` or `KBrO_3` or `KI` to `KIO_3`

Answer

To understand why concentrated sulfuric acid (H₂SO₄) cannot be used to prepare HBr or HI from KBr or KI, we need to analyze the properties of sulfuric acid and the reactions involved. Here’s a step-by-step breakdown of the reasoning:

### Step 1: Understand the Reaction
When concentrated sulfuric acid is added to potassium bromide (KBr) or potassium iodide (KI), it is expected to produce hydrobromic acid (HBr) or hydroiodic acid (HI), respectively.

### Step 2: Identify the Properties of Sulfuric Acid
Sulfuric acid has several important properties:
- **Acidic Nature**: It can donate protons (H⁺).
- **Oxidizing Nature**: It can accept electrons and oxidize other substances.
- **Dehydrating Nature**: It can remove water from substances.
- **Sulphonation**: It can introduce sulfonyl groups into organic compounds.

### Step 3: Analyze the Oxidizing Nature
The key property that affects the reaction with KBr and KI is the oxidizing nature of concentrated sulfuric acid. When H₂SO₄ comes into contact with KBr or KI, it acts as an oxidizing agent.

### Step 4: Determine the Reaction Products
- For KBr: The bromide ion (Br⁻) in KBr has an oxidation state of -1. When it reacts with concentrated H₂SO₄, it gets oxidized to bromine (Br₂), where the oxidation state is 0.
- For KI: Similarly, the iodide ion (I⁻) in KI is oxidized to iodine (I₂) when it reacts with concentrated H₂SO₄.

### Step 5: Conclusion
Since H₂SO₄ oxidizes Br⁻ to Br₂ and I⁻ to I₂, it does not produce HBr or HI as expected. Therefore, concentrated sulfuric acid cannot be used to prepare HBr or HI from KBr or KI because it oxidizes these halides instead of producing the corresponding acids.

### Final Answer
Concentrated H₂SO₄ cannot be used to prepare HBr or HI from KBr or KI because it oxidizes KBr to Br₂ and KI to I₂.

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