Correct (2):Hg22+>Cd22+>Zn22+Due to ineffective shielding of 4f electrons, bond strength is maximum for Hg22+ i.e., Hg⊕−Hg⊕Explanation:(1) Due to high lattice or high bond energy for the higher covalent compounds e.g.; in CrF6 and VF6.(3) Along the 3d series. size decreases, due to increase in Zeff.(4) Due to ability of oxygen to form (pπ- dπ) mtltiple bonding, i.e., vacant 3d orbitals of Mn overlap with 2p orbitals of oxygen.