(i)-(d), (ii)-(a), (iii)-(b), (iv)-(e), (v)-(f)

(i)-(d)FeSO₄.7H₂O, Fe²⁺ has 3d⁶ electronic configuration. The complementary colour is pale green

(ii)-(a) NiCl₂.4H₂O ,Ni²⁺ has 3d⁸ electronic configuration. The complementary colour is green

(iii)-(b)MnCl₂.4H₂O , Mn²⁺ has 3d⁵ electronic configuration. The complementary colour is light pink

(iv)-(e)CoCl₂.6H₂O, Co²⁺ has 3d⁷ electronic configuration. The complementary colour is pink

(v)-(f) Cu₂Cl₂is colourless, Cu⁺ has 3d¹⁰ electronic configuration. It has a fully filled d orbital without no unpaired electrons to get excited and absorb visible light. So, Cu₂Cl₂ is colourless.