The most acidic hydrogen atoms are present in

Options

A. Ethane
B. ethene
C. ethyne
D. benzene

Answer

To determine which compound has the most acidic hydrogen atoms, we need to analyze the structures of the given hydrocarbons and their corresponding acidic hydrogen atoms.

### Step 1: Identify the Hydrocarbons
The hydrocarbons mentioned are:
1. Ethane (C2H6)
2. Ethene (C2H4)
3. Ethyne (C2H2)
4. Benzene (C6H6)

### Step 2: Understand Acidity in Hydrocarbons
The acidity of hydrogen atoms in hydrocarbons is influenced by the stability of the resulting carbanion when the hydrogen is removed (deprotonation). The more stable the carbanion, the more acidic the hydrogen atom is.

### Step 3: Analyze Each Hydrocarbon
1. **Ethane (C2H6)**: The hydrogen atoms are attached to sp3 hybridized carbons. The resulting carbanion (C2H5-) is relatively unstable.

2. **Ethene (C2H4)**: The hydrogen atoms are attached to sp2 hybridized carbons. The resulting carbanion (C2H3-) is more stable than that of ethane but less stable than that of ethyne.

3. **Ethyne (C2H2)**: The hydrogen atoms are attached to sp hybridized carbons. The resulting carbanion (C2H-) is very stable due to the high electronegativity of sp hybridized carbon, which holds the negative charge more effectively.

4. **Benzene (C6H6)**: The hydrogen atoms are also attached to sp2 hybridized carbons. The resulting carbanion (C6H5-) is stabilized by resonance, but it is still less stable than the carbanion formed from ethyne.

### Step 4: Compare the Stability of Carbanions
- The stability of carbanions decreases in the order:
- sp > sp2 > sp3
- Therefore, the carbanion formed from ethyne (sp hybridized) is the most stable.

### Step 5: Conclusion
Since the most stable carbanion corresponds to the most acidic hydrogen, the most acidic hydrogen atoms are present in **ethyne (C2H2)**.

### Final Answer
The most acidic hydrogen atoms are present in **ethyne (C2H2)**.

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