(i) Cu2+ salts are coloured whereas Zn2+ salts are white because Cu2+([Ar]3d9) has one unpaired electron in d-orbital which allows electron transition in visible region which imparts colour whereas Zn2+([Ar]3d10) do not possess any unpaired electron hence no electron transition takes place thus shows no colour.
(ii) E∘ values for Mn3+∕Mn2+ couple is much more positive than for Cr3+∕Cr2+ because the conversion of Mn2+ from Mn3+ possesses extra stability due to half filled valence electronic configuration (3d5) whereas Cr ion changes from Cr3+ to Cr2+ undergoes change in outer configuration from 3dβ to 3d4 making it less stable comparatively.
(iii) Transition metals have very similar atomic sizes as a result one metal can easily replace the other metal from its lattice to form solid solution (alloy). Transition metals are also miscible with one another in the molten state. Thus, the molten state solution of two or more transition metals on cooling forms alloy.