Transition elements and their compounds are found to be good catalysts. Give examples.

Explanation

Transition elements show catalytic properties due to the presence of partially filled d-subshells. They form unstable intermediate products with reactants. These intermediates increase the rate of reaction. For example, in the conversion of `SO_2` to `SO_3` , vanadium pentoxide is used as a catalyst as:
`underset("catalyst")(SO_2 + V_2O_5) to underset("intermediate")(SO_3+V_2O_4)`
`2V_2O_4 + O_2 to 2V_2 O_5`
In this case vanadium with variable oxidation states gives an intermediate with the reactant.