Explain why :
Transition metals and their compounds act as catalyst.

Explanation

The transition metals and their compounds are known for their catalytic activity because they have ability to adopt multiple oxidation states they have variable oxidation state giving unstable intermediates and can form complexes. Catalysts at a solid surface involves the formation of bonds between reactant molecules and atoms of the surface of the catalyst, thus increasing the concentration of the reactants at the catalyst surface and also weakening of the bonds in the reactant molecules thus lowering the activation energy and facilitating the reaction.