In PCl5 Phosphorus Pentachloride , the central atom is phosphorus P . To determine the hybridization of the central atom, we need to consider the number of electron domains around it.Phosphorus has 5 valence electrons, and each chlorine atom contributes one electron. Therefore, there are a total of 5 + 5 = 10 electrons around the central phosphorus atom. These electrons are distributed in 5 electron domains 5 P-Cl bonds .According to the VSEPR Valence Shell Electron Pair Repulsion theory, the electron domains will arrange themselves to minimize repulsion. In this case, the electron domains form a trigonal bipyramidal arrangement.To accommodate 5 electron domains, the central phosphorus atom undergoes hybridization, which is the mixing of atomic orbitals to form new hybrid orbitals. In this case, one s orbital, three p orbitals, and one d orbital from the third shell mix to form five sp3d hybrid orbitals.So, the hybridization of the central atom phosphorus in PCl5 is sp3d.