Acidic hydrogen is present in:

Options

A. (a) Ethyne
B. (b) Ethene
C. (c) Benzene
D. (d) Ethane

Explanation

To determine which compound has acidic hydrogen, we need to analyze the structures of the given options and understand the concept of acidic hydrogen. Acidic hydrogen is defined as a hydrogen atom that can be removed from a molecule, resulting in a stable negative charge (conjugate base).

### Step-by-Step Solution:

1. **Identify the Compounds**:
- A) Ethane (C2H6)
- B) Ethene (C2H4)
- C) Benzene (C6H6)
- D) Ethyne (C2H2)

2. **Draw the Structures**:
- Ethane: CH3-CH3
- Ethene: CH2=CH2
- Benzene: C6H6 (ring structure with alternating double bonds)
- Ethyne: HC≡CH

3. **Understand Acidic Hydrogen**:
- Acidic hydrogen is one that can be removed to form a stable conjugate base. The stability of the conjugate base is influenced by the hybridization of the carbon atom to which the hydrogen is attached.
- The order of acidity based on hybridization is: sp > sp2 > sp3. This means that hydrogen attached to sp hybridized carbon is the most acidic.

4. **Analyze Each Compound**:
- **Ethane (C2H6)**: All hydrogens are attached to sp3 hybridized carbons. Removal of a hydrogen would result in a highly unstable negative charge on an sp3 carbon. Thus, it does not have acidic hydrogen.
- **Ethene (C2H4)**: The hydrogen is attached to sp2 hybridized carbons. Removal of a hydrogen would result in a negative charge on an sp2 carbon, which is more stable than sp3 but less than sp.
- **Benzene (C6H6)**: The hydrogens are attached to sp2 hybridized carbons. Similar to ethene, removal of a hydrogen would result in a negative charge on an sp2 carbon.
- **Ethyne (C2H2)**: The hydrogen is attached to sp hybridized carbons. Removal of a hydrogen would result in a negative charge on an sp carbon, which is the most stable.

5. **Conclusion**:
- The compound that has acidic hydrogen is **Ethyne (C2H2)**, as it has sp hybridized carbons, making the hydrogen attached to it the most acidic.

### Final Answer:
The correct option is **D) Ethyne**.