Consider the following substances
1. `CH_(3)C-= C CH_(3)`
2. `CH_(3)CH_(2)C-=CH`
3. `CH_(3)CH=CHCH_(3)`
4. `CH_(3)CH_(2)CH=CH_(2)`
Which of the following reagent can be used to distinguish the compound (2) from the rest of the compounds?

Options

A. Bromin/ `"CCl"_(4)`
B. Bromine/`CH_(3)COOH`
C. `Alk.KMnO_(4)`
D. Ammonical `AgNO_(3)` or ammoniacal cuprous chloride

Answer

To distinguish compound (2) from the other compounds, we need to analyze the structures of the given compounds and identify a suitable reagent that can differentiate them based on their functional groups.

### Step-by-Step Solution:

1. **Identify the Compounds**:
- Compound (1): `CH₃C≡CCH₃` (2-butyne, an internal alkyne)
- Compound (2): `CH₃CH₂C≡CH` (1-butyne, a terminal alkyne)
- Compound (3): `CH₃CH=CHCH₃` (butene, an alkene)
- Compound (4): `CH₃CH₂CH=CH₂` (butene, an alkene)

2. **Determine the Functional Groups**:
- Compounds (1) and (2) are alkynes (specifically, compound (2) is a terminal alkyne).
- Compounds (3) and (4) are alkenes.

3. **Select a Suitable Reagent**:
- We need a reagent that can distinguish between terminal alkynes and internal alkynes or alkenes.
- A common reagent for this purpose is **ammoniacal silver nitrate (AgNO₃ in ammonia)** or **ammonical cuprous chloride (CuCl in ammonia)**.

4. **Reaction with Ammoniacal Silver Nitrate**:
- Terminal alkynes react with ammoniacal silver nitrate to form a red precipitate of silver acetylide.
- Internal alkynes and alkenes do not react in the same way and do not produce this precipitate.

5. **Conclusion**:
- Since compound (2) is a terminal alkyne, it will react with ammoniacal silver nitrate to give a red precipitate, while the other compounds (1, 3, and 4) will not.
- Therefore, the reagent that can be used to distinguish compound (2) from the rest is **ammoniacal silver nitrate (or ammonical cuprous chloride)**.

### Final Answer:
The reagent that can be used to distinguish compound (2) from the rest is **ammoniacal silver nitrate (AgNO₃ in ammonia)**.

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