Solved Examples for JEE: The d & f- Block Elements (Transition Elements) | Mock Tests for JEE Main and Advanced 2026 PDF Download

Question 1: Ti(H₂O)₆]³⁺ is coloured whereas  [Sc(H­₂O)₆]³⁺ is colourless, though it is a transition metal complex. Explain the observation.
Solution: Ti³⁺ has one electron in the d-orbital (3d¹) which can absorb energy corresponding to yellow wavelength and jump from lower energy level to higher energy level. But Sc³⁺ has no electron in d-orbital.

Question 2: NiCl₄]^2– is paramagnetic while (Ni(CO)₄] is diamagnetic. Why?
Solution: In [Ni(CO)₄], Ni is in zero oxidation state whereas is (NiCl₄]^2–, Ni is in +2 oxidation state. In the presence of ligand CO, the unpaired electrons of Ni pair up but Cl– being a weak ligand is unable to pair up the unpaired electrons.

Question 3: Calculate the magnetic moment of V³⁺.
Solution: The electronic configuration of V³⁺ is [Ar] 4s°3d². In the d–orbitals there are 2 unpaired electrons

Question 4: Why Sm²⁺, Eu²⁺ and Yb²⁺ ions in solutions are good reducing agents but an aqueous solution of Ce⁴⁺ is a good oxidizing agent?
Solution: The most stable oxidation state of lanthanides is +3 hence ions in +2 state tend to change to +3 state by loss of electron and those in+4 state tend to change to +3 state by gain of electron