The number of compounds having all atoms in a single plane are
`XeF_(4),SF_(4), Al_(2)Cl_(6),SnCl_(4),I_(2)Cl_(6), H_(2)C=C=C=CH_(2), PhCl, C_(2)(CN)_(4),ICl_(3), PCl_(5)`

Answer

To determine the number of compounds having all atoms in a single plane from the given list, we will analyze each compound one by one based on their molecular geometry and hybridization.

### Step-by-Step Solution:

1. **XeF4 (Xenon Tetrafluoride)**:
- Xenon has 8 valence electrons. It forms 4 bonds with fluorine atoms and has 2 lone pairs.
- The hybridization is sp³d², leading to an octahedral shape. The lone pairs occupy axial positions, resulting in a square planar geometry.
- **Conclusion**: Planar.

2. **SF4 (Sulfur Tetrafluoride)**:
- Sulfur has 6 valence electrons. It forms 4 bonds with fluorine and has 1 lone pair.
- The hybridization is sp³d, leading to a seesaw shape. The lone pair occupies an equatorial position, making it non-planar.
- **Conclusion**: Non-planar.

3. **Al2Cl6 (Aluminum Hexachloride)**:
- Aluminum has 3 valence electrons. In Al2Cl6, aluminum forms coordinate bonds with chlorine.
- The structure is planar due to the presence of pi bonds between the aluminum and chlorine.
- **Conclusion**: Planar.

4. **SnCl4 (Tin Tetrachloride)**:
- Tin has 4 valence electrons. It forms 4 bonds with chlorine atoms.
- The hybridization is sp³, leading to a tetrahedral shape.
- **Conclusion**: Non-planar.

5. **I2Cl6 (Dichlorine Hexachloride)**:
- Iodine has 7 valence electrons. In I2Cl6, iodine forms bonds with chlorine.
- The structure is planar due to the arrangement of the atoms.
- **Conclusion**: Planar.

6. **H2C=C=C=CH2 (Butatriene)**:
- This compound has alternating double bonds between carbon atoms.
- All hydrogen and carbon atoms lie in the same plane due to the nature of double bonds.
- **Conclusion**: Planar.

7. **PhCl (Chlorobenzene)**:
- The benzene ring is planar, and the chlorine atom is attached to it.
- **Conclusion**: Planar.

8. **C2(CN)4 (Dicyanobutadiene)**:
- The structure involves a linear arrangement of carbon and nitrogen atoms.
- All atoms are in the same plane.
- **Conclusion**: Planar.

9. **ICl3 (Iodine Trichloride)**:
- Iodine has 7 valence electrons. It forms 3 bonds with chlorine and has 2 lone pairs.
- The hybridization is sp³d, leading to a T-shaped geometry. The T-shape is planar.
- **Conclusion**: Planar.

10. **PCl5 (Phosphorus Pentachloride)**:
- Phosphorus has 5 valence electrons. It forms 5 bonds with chlorine.
- The hybridization is sp³d, leading to a trigonal bipyramidal shape. This structure is non-planar.
- **Conclusion**: Non-planar.

### Summary of Planar Compounds:
- Planar Compounds: XeF4, Al2Cl6, I2Cl6, H2C=C=C=CH2, PhCl, C2(CN)4, ICl3
- Total Planar Compounds: 7

### Final Answer:
The number of compounds having all atoms in a single plane is **7**.