Amongst, NiCl42−,Cu2Cl2,ScF63− and CoF63−, the coloured species are

(i) Sc⁡(Z=21),3d14s2Sc+3=3d04s0⇒ Colourless  (ii) Co⁡(Z=24),3d54s2Co+3=3d44s0⇒ Coloured  (iii) Ni(Z=28),3d64s2Ni+2=3d64s0⇒ Colouress  (iv) Cu(Z=29),3d104s1Cu+1=3d104s0⇒ Colourless Formation of coloured compound is due to excitation of e-'s from  orbitals t2g to eg orbitals.