Hydrocarbon 'A' reacts with `KMnO_4` under neutral conditions at room temperature to form only a diketone,
`CH_3CH_2underset(O)underset(||)C-underset(O)underset(||)C"CH"_2CH_2CH_3`. The hydrocarbon is

Options

A. `CH_3C-="CCH"_2CH_2CH_2CH_3`
B. `HC-="CCH"_2CH_2CH_2CH_2CH_3`
C. `CH_3C-=underset(CH_3)underset(|)C"CHCH"_2CH_3`
D. `CH_3CH_2C-="CCH"_2CH_2CH_3`

Answer

To solve the problem, we need to identify the hydrocarbon 'A' that reacts with KMnO4 under neutral conditions to form the given diketone. The diketone is represented as:

\[ \text{CH}_3\text{CH}_2\text{C}=\text{C}=\text{CH}_2\text{CH}_2\text{CH}_3 \]

### Step-by-Step Solution:

1. **Understand the Reaction**: KMnO4 in neutral conditions is known to oxidize alkynes to diketones. This means that the hydrocarbon 'A' must be an alkyne, specifically one that has a triple bond.

2. **Identify the Structure of the Diketone**: The diketone provided can be broken down into its structural components. The structure indicates that it has two carbonyl (C=O) groups, which means that the original hydrocarbon 'A' must have a triple bond between two carbon atoms that will be oxidized to form these carbonyl groups.

3. **Determine the Position of the Triple Bond**: The diketone has the following structure:
\[ \text{CH}_3\text{CH}_2\text{C}=\text{C}=\text{O}\text{O}\text{CH}_2\text{CH}_2\text{CH}_3 \]
This suggests that the triple bond is between the third and fourth carbon atoms in the chain, making it a symmetrical alkyne.

4. **Construct the Hydrocarbon 'A'**: To form the diketone, the hydrocarbon 'A' must be:
\[ \text{CH}_3\text{CH}_2\text{C} \equiv \text{C}\text{CH}_2\text{CH}_2\text{CH}_3 \]
This structure indicates that 'A' is 1-heptyne, which has the formula C7H14.

5. **Verify the Options**: Check the provided options to see which one corresponds to 1-heptyne. The correct hydrocarbon should have the structure that allows for the formation of the diketone upon oxidation with KMnO4.

6. **Conclusion**: The hydrocarbon 'A' that reacts with KMnO4 to produce the given diketone is 1-heptyne.

### Final Answer:
The hydrocarbon 'A' is **1-heptyne** (C7H14).