Paramagnetic character is based upon the presence of unpaired electrons in d-subshell. In these complex ions. (a) In [Cr(H2O6]3+,Cr is present as Cr3+ (Oxidation number =+3) Cr3+=1s22s22p63s23p63d3
(b) In [Fe(H2O6]2+, Fe is present as Fe2+=1s22s22p63s23p63d6
(c) In [Cu(H2O)6]2+,Cu is present as Cu2+ Cu2+=1s22s22p63s23p63d9
(d) In[Zn(H2O)2]2+,Zn is present as Zn2+=1s22s22p63s23p63d10
In complex (a), (b) and (c) have unpaired electrons, so they show propercy of paramagnetism. Paramangetic character ∝ Number of unpaired electron. So, paramagnetic character is maximum in [Fe(H2O)6]2+.