Which of the following element will exhibit maximum tendency of forming pp–dp bonding in theiroxoanions?

Cl has the highest propensity for p-d-p-d bonding among the listed elements. Nuclear charge rises when the period is crossed, and additional s and p electrons are added. The atomic size and subsequently the size of 3d-orbitals drop from Si, P, S, and Cl due to insufficient nuclear charge shielding. Si→P→S→Cl. A smaller 3d-orbital results in a stronger pdp-d overlap.