Number of molecules with p-d bonding:

1. P4O10:
- P4O10 is a covalent compound composed of four phosphorus atoms and ten oxygen atoms.
- In P4O10, each phosphorus atom is bonded to three oxygen atoms through a double bond, resulting in a total of 12 p-d bonds.
- Therefore, P4O10 has 12 p-d bonds.

2. N2O5:
- N2O5 is a covalent compound composed of two nitrogen atoms and five oxygen atoms.
- In N2O5, each nitrogen atom is bonded to two oxygen atoms through a double bond, resulting in a total of four p-d bonds.
- Therefore, N2O5 has four p-d bonds.

3. (SiH3)3N:
- (SiH3)3N is a covalent compound composed of three silicon atoms, nine hydrogen atoms, and one nitrogen atom.
- In (SiH3)3N, the silicon atoms are covalently bonded to the nitrogen atom through three Si-N bonds.
- Since the bonding in (SiH3)3N involves p-orbitals of silicon and nitrogen, there are three p-d bonds present.
- Therefore, (SiH3)3N has three p-d bonds.

4. SO3:
- SO3 is a covalent compound composed of one sulfur atom and three oxygen atoms.
- In SO3, the sulfur atom is bonded to three oxygen atoms through a double bond and a coordinate covalent bond.
- The coordinate covalent bond involves the donation of an electron pair from one of the oxygen atoms to the sulfur atom, resulting in a p-d bond.
- Therefore, SO3 has one p-d bond.

In summary, the number of molecules among P4O10, N2O5, (SiH3)3N, and SO3 that have p-d bonding is three: P4O10, N2O5, and (SiH3)3N.