Explain giving reasons :
Transition metals and their many compounds act as good catalyst.

Explanation

The catalytic activity of transition metals and many of their compounds may be due to the following reasons : (i) Transition metals with their variable valencies may form unstable intermediates with the reacting molecules, providing a new path of lower activation energy for the reaction. (ii) Transition metals provide large surface area with free valencies on which reactant molecules get absorbed. This has the effect of increasing concentration of reactants on catalyst surface and also weakening of bonds in reacting molecules. This lowers the activation energy and makes the reaction proceed faster.