`CH_(3) - CH(Cl) - C_(2)H_(5) overset(Alc.KOH)(rarr) CH_(3) - CH = CH - CH_(3)`
The above reaction proceeds via `ElcB` mechanism. Which of the followiing statements is true about `ElcB` mechanism?

Options

A. It is secound order and bimolecular.
B. It is first order and unimolecular.
C. It is first order and unimolecular.
D. It is secound order of unimolecular.

Explanation

To solve the question regarding the `ElcB` mechanism and determine which statement is true about it, we will break down the process step by step.

### Step-by-Step Solution:

1. **Understanding the Reaction**:
The given reaction is between an alkyl halide (specifically, CH₃-CH(Cl)-C₂H₅) and alcoholic KOH, which leads to the formation of an alkene (CH₃-CH=CH-CH₃). This reaction is indicated to proceed via the `ElcB` mechanism.

**Hint**: Identify the reactants and products to understand the type of reaction taking place.

2. **Formation of the Conjugate Base**:
In the `ElcB` mechanism, the first step involves the deprotonation of the alpha carbon (the carbon adjacent to the carbon bearing the leaving group, Cl in this case) by a strong base (OH⁻). This results in the formation of a conjugate base.

**Hint**: Remember that the alpha carbon is crucial in the `ElcB` mechanism.

3. **Slow Step of the Mechanism**:
After the formation of the conjugate base, the next step is the elimination of the leaving group (Cl⁻) to form the alkene. This step is the rate-determining step (slow step) of the reaction.

**Hint**: The slow step is critical in determining the rate of the reaction.

4. **Unimolecular Nature**:
The slow step involves only one molecule (the conjugate base), making the reaction unimolecular in this step. The rate of the reaction is dependent on the concentration of the conjugate base.

**Hint**: Consider how the rate of reaction is influenced by the concentration of reactants.

5. **Rate Expression**:
The rate of the reaction can be expressed as:
\[ \text{Rate} = k \cdot [\text{Conjugate Base}] \]
Since the formation of the conjugate base depends on both the base (OH⁻) and the alkyl halide, the overall reaction can be considered second order (first order with respect to the conjugate base and first order with respect to the alkyl halide).

**Hint**: Pay attention to how the concentrations of reactants affect the overall order of the reaction.

6. **Conclusion**:
Based on the analysis, the statements regarding the `ElcB` mechanism that are true include:
- The mechanism involves the formation of a conjugate base.
- The rate-determining step is unimolecular.
- The overall reaction is second order due to the dependence on both the base and the alkyl halide.

**Final Answer**: The correct statement about the `ElcB` mechanism is that it is a second-order unimolecular reaction.