How many of the following compounds have significant involvement of d orbital in p bonding ?
`H_2PO_2, BCl_3, H_2S_4O_6,XeO_6, XeOF_4, Fe(CO)_5,SF_6, NH_4Cl, ClO_2, NO_2`.

Explanation

To determine how many of the given compounds have significant involvement of d orbitals in p bonding, we will analyze each compound one by one.

### Step-by-Step Solution:

1. **H₂PO₂ (Phosphorous Acid)**
- Structure: Phosphorus (P) is the central atom bonded to two hydroxyl groups (OH) and one double-bonded oxygen (O).
- Bonding: In H₂PO₂, there is d-pi, p-pi bonding due to the presence of the double bond between P and O.
- **Conclusion**: **Counted** (1 compound).

2. **BCl₃ (Boron Trichloride)**
- Structure: Boron (B) is the central atom bonded to three chlorine (Cl) atoms.
- Bonding: In BCl₃, there is p-pi, p-pi back bonding, but no involvement of d orbitals.
- **Conclusion**: **Not counted** (0 compounds).

3. **H₂S₄O₆ (Thiosulfuric Acid)**
- Structure: Contains sulfur atoms (S) bonded with oxygen (O) and hydroxyl (OH) groups.
- Bonding: There is d-pi, p-pi bonding due to the double bonds between S and O.
- **Conclusion**: **Counted** (2 compounds).

4. **XeO₆ (Xenon Hexoxide)**
- Structure: Xenon (Xe) is bonded to six oxygen atoms, with some double bonds.
- Bonding: There is d-pi, p-pi bonding due to the presence of double bonds between Xe and O.
- **Conclusion**: **Counted** (3 compounds).

5. **XeOF₄ (Xenon Oxyfluoride)**
- Structure: Xenon (Xe) is bonded to one oxygen and four fluorine atoms.
- Bonding: There is d-pi, p-pi bonding due to the double bond between Xe and O.
- **Conclusion**: **Counted** (4 compounds).

6. **Fe(CO)₅ (Iron Pentacarbonyl)**
- Structure: Iron (Fe) is bonded to five carbon monoxide (CO) ligands.
- Bonding: Metal carbonyls like Fe(CO)₅ involve d-orbitals in pi bonding.
- **Conclusion**: **Counted** (5 compounds).

7. **SF₆ (Sulfur Hexafluoride)**
- Structure: Sulfur (S) is bonded to six fluorine (F) atoms.
- Bonding: There are no pi bonds present in SF₆.
- **Conclusion**: **Not counted** (5 compounds).

8. **NH₄Cl (Ammonium Chloride)**
- Structure: Ammonium (NH₄) is a cation bonded to a chloride ion (Cl⁻).
- Bonding: There are no pi bonds present in NH₄Cl.
- **Conclusion**: **Not counted** (5 compounds).

9. **ClO₂ (Chlorine Dioxide)**
- Structure: Chlorine (Cl) is bonded to two oxygen atoms, one with a double bond.
- Bonding: There is d-pi, p-pi bonding due to the double bond between Cl and O.
- **Conclusion**: **Counted** (6 compounds).

10. **NO₂ (Nitrogen Dioxide)**
- Structure: Nitrogen (N) is bonded to two oxygen atoms.
- Bonding: There are no d-orbitals involved in bonding.
- **Conclusion**: **Not counted** (6 compounds).

### Final Count:
- Total compounds with significant involvement of d orbitals in p bonding: **6**

### Answer:
**6 compounds have significant involvement of d orbitals in p bonding.**