Which is the most suitable reagent among the following to distinguish compound (iii) from the rest of the compounds
i. `CH_(3)-C-=C-CH_(3)`
ii. `CH_(2)-CH_(2)-CH_(2)-CH_(3)`
iii. `CH_(3)-CH_(2)-C-=CH`
iv. `CH_(3)-CH=CH_(2)`

Options

A. `Br_(2)" in CCl"_(4)`
B. Cold aqueous alkaline `KMnO_(4)`
C. Ammonical `AgNO_(3)` solution
D. `OsO_(4)`

Answer

To solve the problem of distinguishing compound (iii) from the rest of the compounds, we need to analyze the given compounds and identify the suitable reagent.

### Step-by-Step Solution:

1. **Identify the Compounds:**
- Compound (i): `CH₃-C≡C-CH₃` (2-butyne, a terminal alkyne)
- Compound (ii): `CH₂-CH₂-CH₂-CH₃` (butane, an alkane)
- Compound (iii): `CH₃-CH₂-C≡CH` (1-butyne, a terminal alkyne)
- Compound (iv): `CH₃-CH=CH₂` (propene, an alkene)

2. **Recognize the Type of Compound:**
- Compound (iii) is a terminal alkyne, which means it has a triple bond at the end of the carbon chain.

3. **Determine the Reagent for Distinction:**
- Terminal alkynes can be distinguished from other types of hydrocarbons using specific reagents. One such reagent is ammoniacal silver nitrate (AgNO₃ in NH₄OH).

4. **Reaction of Terminal Alkyne with Ammoniacal Silver Nitrate:**
- When a terminal alkyne reacts with ammoniacal silver nitrate, it forms a white precipitate of silver acetylide. The reaction can be represented as:
\[ CH₃-CH₂-C≡CH + AgNO₃ \rightarrow CH₃-CH₂-C≡C^{-}Ag^{+} + NH₄^{+} \]
- The formation of a white precipitate indicates the presence of a terminal alkyne.

5. **Conclusion:**
- Therefore, the most suitable reagent to distinguish compound (iii) from the rest is ammoniacal silver nitrate (AgNO₃ in NH₄OH).

### Final Answer:
The most suitable reagent to distinguish compound (iii) from the rest is ammoniacal silver nitrate (AgNO₃ in NH₄OH).