In the presence of platinum catalyst, hydrocarbon (A) adds hyrogen to form n-hexane. When hydrogen bromide is added to (A) instead of hydrogen, only a single bromo compound is formed. Which of the following is (A)?

Options

A. `H_(2)C=CH-CH_(2)-CH_(2)-CH_(2)`
B. `CH_(3)-CH=CH-CH_(2)-CH_(2)-CH_(3)`
C. `CH_(3)-CH_(2)-CH=CH-CH_(2)-CH_(3)`
D. `CH_(3)-CH_(2)-CH_(2)-CH=CH-CH_(3)`

Answer

To determine the structure of hydrocarbon (A), we need to analyze the information given in the question carefully.

### Step 1: Understand the Reaction with Hydrogen
The question states that hydrocarbon (A) adds hydrogen in the presence of a platinum catalyst to form n-hexane.
- n-Hexane has the molecular formula C6H14, which indicates that (A) must be an unsaturated hydrocarbon (alkene or alkyne) that can be hydrogenated to form n-hexane.

### Step 2: Determine the Structure of (A)
Since n-hexane has 6 carbon atoms and is fully saturated (no double or triple bonds), (A) must have at least one double bond (alkene) or triple bond (alkyne) that can be converted to a single bond by adding hydrogen.

### Step 3: Analyze the Reaction with Hydrogen Bromide
The question also states that when hydrogen bromide (HBr) is added to (A), only a single bromo compound is formed.
- This indicates that (A) must have a symmetrical structure, so that the addition of HBr leads to only one possible product.

### Step 4: Identify Possible Structures
For a compound to yield only one bromo compound upon addition of HBr, it should preferably be a symmetrical alkene.
- The simplest symmetrical alkene with 6 carbon atoms is 2-hexene (C6H12), which has the structure CH3-CH=CH-CH2-CH2-CH3.

### Step 5: Confirm the Structure
1. **Hydrogenation**: When 2-hexene is hydrogenated, it will convert to n-hexane (C6H14).
2. **Addition of HBr**: When HBr is added to 2-hexene, it can only add across the double bond in one way, resulting in 2-bromohexane (C6H13Br), which is the only product.

### Conclusion
Based on the above analysis, the hydrocarbon (A) is **2-hexene**.