Alkene can be prepared from alkyl halide by the following reagent `R-X+Nu^(-) to ` Alkene + NuH

Options

A. Alc. KOH heat
B. Aq. KOH + cold water
C. NaOH
D. LiOH

Answer

To prepare an alkene from an alkyl halide using a nucleophile, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Alkyl Halide**: Start with an alkyl halide represented as R-X, where R is an alkyl group and X is a halogen (Cl, Br, or I).

2. **Choose the Nucleophile**: Select a suitable nucleophile for the reaction. In this case, we will use alcoholic KOH (potassium hydroxide in alcohol).

3. **Understand the Reaction Mechanism**: The reaction involves a process called dehydrohalogenation. This means that a hydrogen atom and a halogen atom will be removed from the alkyl halide to form an alkene.

4. **Write the Reaction**: The general reaction can be written as:
\[ R-X + \text{KOH (alc)} \rightarrow \text{Alkene} + \text{KX} + \text{H}_2\text{O} \]
Here, KX represents the potassium halide formed as a byproduct.

5. **Determine the Alkene Structure**: When the halogen (X) is eliminated, a double bond forms between the carbon atoms adjacent to the halogen. For example, if we start with CH3-CH2-Cl (ethyl chloride), the reaction will produce ethylene (CH2=CH2).

6. **Byproducts Formation**: The hydrogen atom that is removed during the reaction will combine with the hydroxide ion (OH-) from KOH to form water (H2O).

7. **Final Reaction Example**:
\[ \text{CH}_3\text{CH}_2\text{Cl} + \text{KOH (alc)} \rightarrow \text{CH}_2=CH_2 + \text{KCl} + \text{H}_2\text{O} \]

### Conclusion:
The alkene is formed by the elimination of HX (where X is the halogen) from the alkyl halide in the presence of alcoholic KOH.