The compound having maximum number of `p pi-dpi` bonds is :

Options

A. `SO_(2)`
B. `H_(2)SO_(4)`
C. `HNO_(3)`
D. `HClO_(4)`

Explanation

To determine the compound with the maximum number of pπ-dπ bonds among the given options (SO2, H2SO4, HNO3, and HClO4), we will analyze each compound step by step.

### Step 1: Analyze SO2
- **Composition**: SO2 consists of sulfur (S) and oxygen (O).
- **Valence Electrons**: Sulfur has 6 valence electrons, and each oxygen has 6 valence electrons.
- **Bonding**: Sulfur forms two double bonds with the two oxygen atoms.
- **Hybridization**: The hybridization of sulfur in SO2 is sp² (2 bond pairs and 1 lone pair).
- **pπ-dπ Bonds**: There is 1 pπ-dπ bond formed between sulfur and one of the oxygen atoms.

### Step 2: Analyze H2SO4
- **Composition**: H2SO4 consists of sulfur (S) and four oxygen (O) atoms.
- **Valence Electrons**: Sulfur has 6 valence electrons.
- **Bonding**: Sulfur forms two double bonds with two oxygen atoms and two single bonds with two hydroxyl groups (OH).
- **Hybridization**: The hybridization of sulfur in H2SO4 is sp³ (4 bond pairs).
- **pπ-dπ Bonds**: There are 2 pπ-dπ bonds (one for each double bond with oxygen).

### Step 3: Analyze HNO3
- **Composition**: HNO3 consists of nitrogen (N) and three oxygen (O) atoms.
- **Valence Electrons**: Nitrogen has 5 valence electrons, and each oxygen has 6 valence electrons.
- **Bonding**: Nitrogen forms one double bond with one oxygen and one single bond with another oxygen and a hydroxyl group (OH).
- **Hybridization**: The hybridization of nitrogen in HNO3 is sp² (1 double bond and 2 single bonds).
- **pπ-dπ Bonds**: There are 0 pπ-dπ bonds since nitrogen does not have d orbitals.

### Step 4: Analyze HClO4
- **Composition**: HClO4 consists of chlorine (Cl) and four oxygen (O) atoms.
- **Valence Electrons**: Chlorine has 7 valence electrons.
- **Bonding**: Chlorine forms four bonds with oxygen (three double bonds and one single bond with OH).
- **Hybridization**: The hybridization of chlorine in HClO4 is sp³ (4 bond pairs).
- **pπ-dπ Bonds**: There are 3 pπ-dπ bonds (one for each double bond with oxygen).

### Conclusion
After analyzing all compounds:
- SO2 has 1 pπ-dπ bond.
- H2SO4 has 2 pπ-dπ bonds.
- HNO3 has 0 pπ-dπ bonds.
- HClO4 has 3 pπ-dπ bonds.

Thus, the compound with the maximum number of pπ-dπ bonds is **HClO4**.

### Final Answer:
**HClO4** (Option D)

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