During the dehydration of alcohols to alkenes by heating with conc. `H_(2)SO_(4)`, the initiating step is `:`

Options

A. Protonation of alcohol molecule
B. Formation of carbocation
C. Elimination of water
D. Formation of an ester

Answer

To solve the question regarding the dehydration of alcohols to alkenes when heated with concentrated sulfuric acid, we can break down the process into clear steps:

### Step-by-Step Solution:

1. **Understanding the Reaction**: The dehydration of alcohols involves the removal of a water molecule (H₂O) from the alcohol, leading to the formation of an alkene. Concentrated sulfuric acid (H₂SO₄) acts as both an acid and a dehydrating agent.

2. **Protonation of Alcohol**: The first step in the mechanism is the protonation of the alcohol. When an alcohol (for example, ethyl alcohol, CH₃CH₂OH) is mixed with concentrated sulfuric acid, the sulfuric acid donates a proton (H⁺) to the alcohol. This step can be represented as:
\[ CH₃CH₂OH + H₂SO₄ \rightarrow CH₃CH₂OH₂⁺ + HSO₄⁻ \]
Here, the hydroxyl group (–OH) of the alcohol becomes protonated to form an oxonium ion (CH₃CH₂OH₂⁺).

3. **Formation of Carbocation**: After the protonation, the oxonium ion is unstable and can lose a water molecule (H₂O). This leads to the formation of a carbocation (a positively charged carbon species). The reaction can be summarized as:
\[ CH₃CH₂OH₂⁺ \rightarrow CH₃CH₂⁺ + H₂O \]
The carbocation is an important intermediate in the reaction.

4. **Deprotonation and Alkene Formation**: Finally, the carbocation can lose a proton (H⁺) to form the alkene. For ethyl alcohol, this results in the formation of ethylene (CH₂=CH₂):
\[ CH₃CH₂⁺ \rightarrow CH₂=CH₂ + H⁺ \]

### Conclusion:
The initiating step in the dehydration of alcohols to alkenes when heated with concentrated sulfuric acid is the **protonation of the alcohol**.