What is a catalyst? Write any one reaction which is brought about by use of caralyst?

Explanation

Catalyst is a substance which increases the rate of a reaction without causing any distrubance to it.
E.g. In the hydrogenation of ethene, nickel or platinum is used as catalyst.
`underset(" Ethene")(H-underset(H)underset(|)C=underset(H)underset(|)C)-H+underset("Hydrogen")(H-H)overset(Ni//Pt)rarrunderset("Ethane")(H-overset(H)overset(|)underset(H)underset(|)C-overset(H)overset(|)underset(H)underset(|)C-H)`