Zirconium (Z = 40) and Hafnium (Z = 72) possess nearly identical atomic and ionic radii. Which of the following is the primary reason for this phenomenon?

Although the +3 oxidation state is most common in lanthanoids, cerium (Z = 58) exhibits a stable +4 oxidation state because:

The calculated 'spin-only' magnetic moment of Ti2+ (3d2) ion is:

Match List I (Transition metal/compound/complex) with List II (Catalytic Role): List I: A. V2O5 B. Fe C. PdCl2 D. Ni complex List II: I. Preparation of ammonia from N2/H2 mixture II. Polymerisation of alkynes III. Preparation of H2SO4 from SO2 (Contact Process) IV. Oxidation of ethyne to ethanal (Wacker process) Choose the correct matching: