Explain giving a suitable reason for each of the following :
(i) Transition metals and their compounds are generally found to be good catalysts.
(ii) Metal-metals bonding is more frequent for the 4d and the 5d series of transitions metals than that for the 3d series.

Explanation

(i) The catalytic property of transition metals is due to their tendency to form reaction intermediates with suitable reactants. These intermediates given reaction paths of lower activation energy and, therefore ,increase te rate of the reaction . These reaction intermediates reading decompose yielding the products and regeneration the original substance. THe transition metals from the these reaction intermediates due to the presence fo vacant orbitals or their tendency to form variable oxidation states.
(ii) For first transition series: sacandium (z=21) to Zinc (Z = 30) 3d -orbitals are gradually filled. For second transition series: Y ttirum (Z = 39) to Cadmium (Z=48)
4d- orbitials are gardually filled.
For third transition series: Landthanum (Z = 57), Hafnium (Z = 72) to Mercury (Z=80) 5d-orbitals are gradually filled.