What is an oxidising agent and a reducing agent and a catalyst?

Answer 1

An oxidizing agent is something that removes one or more electrons from something itself (the oxidizing agent itself gains one or more electrons).

A reducing agent is something that gives electrons to something else (the reducing agent itself looses electrons).

A catalyst is something that speeds up a reaction although the catalyst is not consumed itself in the reaction. The catalyst does this by lowering the activation energy of the reaction.

See the Related Questions to the left for more information about oxidation and reduction reactions and catalysts.