The addition of `HBr` is the easiest with

Options

A. `CH_(2)=CHCl`
B. `ClCH=CHCl`
C. `CH_(3)CH=CH_(2)`
D. `(CH_(3))_(2)C=CH_(2)`

Explanation

To determine which alkene undergoes the addition of HBr most easily, we need to consider the stability of the carbocation that forms during the reaction. The addition of HBr to alkenes proceeds through the formation of a carbocation intermediate, and the stability of this carbocation is a key factor in the reaction's rate.

### Step-by-Step Solution:

1. **Identify the Alkenes**: List the alkenes you are considering for the reaction with HBr. For example, let's say we have propene (CH3-CH=CH2), butene (CH3-CH=CH-CH3), and cyclohexene (C6H10).

2. **Understand Carbocation Formation**: When HBr adds to an alkene, the double bond breaks, and a proton (H+) adds to one of the carbon atoms, leading to the formation of a carbocation on the other carbon. The more stable the carbocation, the easier the addition of HBr will be.

3. **Evaluate Carbocation Stability**:
- **Primary Carbocation**: Least stable (e.g., CH3-CH2-CH2^+)
- **Secondary Carbocation**: More stable (e.g., CH3-CH^+-CH3)
- **Tertiary Carbocation**: Most stable (e.g., (CH3)3C^+)

4. **Analyze Each Alkene**:
- **Propene**: Forms a secondary carbocation upon addition of HBr.
- **Butene**: Can form either a primary or a secondary carbocation, depending on the position of the double bond.
- **Cyclohexene**: Forms a secondary carbocation upon addition of HBr.

5. **Determine the Easiest Addition**: The alkene that forms the most stable carbocation will allow for the easiest addition of HBr. In this case, if we compare the stability of the carbocations formed:
- Propene and cyclohexene both form secondary carbocations.
- Butene can form a primary carbocation, which is less stable.

6. **Conclusion**: The addition of HBr is easiest with alkenes that can form a more stable carbocation. Therefore, between propene, butene, and cyclohexene, the addition of HBr is easiest with propene or cyclohexene due to the formation of secondary carbocations.

### Final Answer:
The addition of HBr is easiest with alkenes that can form secondary or tertiary carbocations, such as propene or cyclohexene.