Which one of the following reagents distinguish ethylene from acetylene?

Options

A. A. Aqueous alkaline `KMnO_4`
B. B. `Cl_2` dissolved in `"CCl"_4`
C. C. Ammoniacal `Cu_2Cl_2`
D. D. conc. `H_2SO_4`

Answer

To distinguish between ethylene (ethene) and acetylene (ethyne), we can analyze their reactions with different reagents. Here’s a step-by-step solution:

### Step 1: Identify the Compounds
- Ethylene (Ethene) is represented as CH2=CH2.
- Acetylene (Ethyne) is represented as CH≡CH.

### Step 2: Analyze the Reagents
We need to find a reagent that can differentiate between these two hydrocarbons. The options provided in the question are likely to include various reagents.

### Step 3: Test with Aqueous KMnO4
- When ethylene is treated with aqueous KMnO4, it undergoes oxidation to form formic acid (HCOOH).
- When acetylene is treated with aqueous KMnO4, it also undergoes oxidation to form oxalic acid (C2H2O4).
- Both reactions decolorize KMnO4 from pink to colorless, meaning KMnO4 cannot distinguish between ethylene and acetylene.

### Step 4: Test with Chlorine in Carbon Tetrachloride
- Chlorine (Cl2) in carbon tetrachloride (CCl4) will react with both ethylene and acetylene through an addition reaction.
- Ethylene will form dichloroethane (CH2Cl-CHCl2) and acetylene will form dichloroacetylene (CHCl=CCl).
- Since both compounds react similarly, chlorine in CCl4 cannot distinguish between them.

### Step 5: Test with Ammonical CuCl2
- Ammonical CuCl2 (cuprous chloride) reacts differently with terminal alkynes (like acetylene) compared to alkenes (like ethylene).
- When ethylene is treated with ammonical CuCl2, there is no reaction.
- When acetylene is treated with ammonical CuCl2, it forms a red precipitate due to the formation of a copper acetylide complex.
- This red precipitate is a clear indication that acetylene is present, thus allowing us to distinguish it from ethylene.

### Step 6: Test with Concentrated H2SO4
- When ethylene reacts with concentrated sulfuric acid (H2SO4), it undergoes electrophilic addition to form ethyl hydrogen sulfate (CH3CH2OSO3H).
- When acetylene reacts with concentrated H2SO4, it also undergoes electrophilic addition but forms a different product.
- However, both compounds react with H2SO4, so this reagent cannot distinguish between them.

### Conclusion
The reagent that can distinguish ethylene from acetylene is **ammonical CuCl2**, as it forms a red precipitate with acetylene but not with ethylene.

### Final Answer
**C. Ammonical CuCl2**