Which of the following compounds is not hydrolysable?

This option is correct because , during the hydrolysis ,  water being neucleophile always prefer to attack the central atom first . it will attack the central atom  only when it posses vacant orbitals . If the central atom doesn't posses vacant orbital then attack  of water molecules taken place on peripheral atom provided they also posses vacant orbitals . in this case niether central nor peripheral atom posses vacant orbital hence hydroysis doesn't takes place in this molecule .