Match List I with List II
| List I: (Property) | List II: (Reason) |
| A. Transition metal can act as catalyst | I. Due to their high ionic charges, small size and availability of d-orbitals |
| B. Zr and Hf have similar atomic radii | II. Unpaired electrons in d-orbitals of metal ions |
| C. Transition metals form complex compounds | III. Ability to adopt multiple oxidation states and to form complexes |
| D. Transition metals ions are coloured | IV. As consequence of Lanthanoid contraction |
Choose the correct answer from the option given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → A-III, B-IV, C-I, D-II
Most special properties of the transition metals come from their partly filled d orbitals and their small, highly charged ions.
A. Transition metal can act as catalyst — This matches III. Ability to adopt multiple oxidation states and to form complexes. A metal that changes its oxidation state easily can take up and give back electrons, and forming complexes with the reactants lowers the activation energy (\( \ce{V2O5} \) in the contact process, Fe in Haber’s process).
B. Zr and Hf have similar atomic radii — This matches IV. As consequence of Lanthanoid contraction. In Hf the 4f subshell, which shields poorly, is filled before the 5d series, so the expected increase in size from Zr (4d) to Hf (5d) is cancelled; both radii are about 160 pm.
C. Transition metals form complex compounds — This matches I. Due to their high ionic charges, small size and availability of d-orbitals. Small, highly charged ions attract ligands strongly, and vacant d orbitals accept their lone pairs.
D. Transition metals ions are coloured — This matches II. Unpaired electrons in d-orbitals of metal ions. A partly filled d subshell allows d–d transitions that absorb visible light.
Shortcut: The pair A-III appears only in Option (3).