Which of the following alkene is most reactive for hydration :-

Options

A. Ethene
B. But-1-ene
C. 2-Methylpropene
D. Propene

Explanation

To determine which alkene is most reactive for hydration, we need to analyze the stability of the carbocations formed during the electrophilic addition reaction of water (H2O) to the alkenes. The more stable the carbocation, the more reactive the alkene will be for hydration.

### Step-by-Step Solution:

1. **Identify the Alkenes**: The alkenes given are:
- Ethene (C2H4)
- But-1-ene (C4H8)
- 2-Methylpropene (C4H8)
- Propene (C3H6)

2. **Draw the Structures**:
- **Ethene**: CH2=CH2
- **But-1-ene**: CH2=CH-CH2-CH3
- **2-Methylpropene**: CH2=C(CH3)-CH3
- **Propene**: CH3-CH=CH2

3. **Understand the Mechanism**: The hydration of alkenes occurs via an electrophilic addition mechanism, where the double bond attacks an electrophile (H+) to form a carbocation intermediate.

4. **Determine the Type of Carbocation Formed**:
- **Ethene**: Forms a primary carbocation (less stable).
- **But-1-ene**: Forms a secondary carbocation (more stable than primary).
- **2-Methylpropene**: Forms a tertiary carbocation (most stable).
- **Propene**: Forms a secondary carbocation (more stable than primary).

5. **Stability of Carbocations**: The stability order of carbocations is:
- Tertiary (3°) > Secondary (2°) > Primary (1°) > Methyl (0°)

6. **Conclusion**: Among the alkenes:
- Ethene forms a primary carbocation.
- But-1-ene and Propene form secondary carbocations.
- 2-Methylpropene forms a tertiary carbocation.

Since the tertiary carbocation is the most stable, **2-Methylpropene** is the most reactive alkene for hydration.

### Final Answer:
**2-Methylpropene** is the most reactive alkene for hydration.

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