The correct option is
B Mn2+<Fe2+<Co2+<Ni2+For a given metal and ligand, the greater the stability the greater the charge on the metal ion. Thus, stability of coordination entities of ions of charge +3 is greater than the entities of +2 ions. For the divalent ions of the first row transition elements, irrespective of the ligand involved, the stabilities vary in the Irving-Williams order:
Mn+2<Fe2+<CO+2<Ni2+<Cu+2>Zn+2