The compound which decolourises bromine water but does not give white precipitate with Tollen's reagent.

Options

A. `C_(2)H_(2)`
B. `C_(2)H_(4)`
C. `C_(6)H_(6)`
D. `CH_(4)`

Answer

To solve the question, "The compound which decolourises bromine water but does not give white precipitate with Tollen's reagent," we need to analyze the properties of different hydrocarbons and their reactions with bromine water and Tollen's reagent.

### Step-by-Step Solution:

1. **Understanding Bromine Water Decolorization**:
- Bromine water is a solution of bromine in water, which is brown in color. Unsaturated hydrocarbons (alkenes and alkynes) can react with bromine, leading to the decolorization of the solution.
- Saturated hydrocarbons (alkanes) and aromatic compounds (like benzene) do not decolorize bromine water.

2. **Identifying Compounds**:
- We need to consider compounds that can decolorize bromine water. Common candidates are alkenes and alkynes.
- For example:
- Ethene (C2H4) is an alkene and can decolorize bromine water.
- Acetylene (C2H2) is an alkyne and can also decolorize bromine water.

3. **Understanding Tollen's Reagent**:
- Tollen's reagent (Ag(NH3)2+) is used to test for aldehydes and some unsaturated compounds. It produces a silver mirror or white precipitate with aldehydes.
- Alkenes do not react with Tollen's reagent to produce a precipitate, while alkynes can sometimes react depending on their structure.

4. **Analyzing the Compounds**:
- Ethene (C2H4):
- Decolorizes bromine water (as it is an alkene).
- Does not give a white precipitate with Tollen's reagent.
- Acetylene (C2H2):
- Decolorizes bromine water.
- Can give a white precipitate with Tollen's reagent under certain conditions.

5. **Conclusion**:
- The compound that decolorizes bromine water but does not give a white precipitate with Tollen's reagent is **C2H4 (Ethene)**.

### Final Answer:
The correct compound is **C2H4 (Ethene)**.

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