Transition Elements

Step 1: Electronic configuration.
- Zn : [Ar] 3d (completely filled d-orbitals).
- Ni : [Ar] 3d (partially filled d-orbitals).
Step 2: Colour and d–d transitions.
- In Zn , no d–d electronic transitions are possible because d-orbitals are completely filled. Hence, Zn salts are colourless.
- In Ni , d–d electronic transitions are possible due to partially filled 3d orbitals. Absorption of visible light during these transitions imparts colour to Ni salts.
Conclusion:
Zn salts are colourless (d , no transitions) while Ni salts are coloured (d , d–d transitions possible).

Step 1: Recall position.
d-block elements are transition metals, lying in groups 3–12. Their valence electrons enter the (n–1)d orbitals.
Step 2: Properties.
- Variable oxidation states due to similar energies of (n–1)d and ns orbitals. - Coloured compounds due to d–d electronic transitions. - Catalytic properties as they provide active sites and variable oxidation states. - Complex formation due to vacant d-orbitals and high charge density.
Step 3: Conclusion.
Thus, d-block elements have distinct properties like variable oxidation states, colour, catalysis, and complex formation.