Oxidising and Reducing Agents

Remember in the previous reaction there was a reaction between zinc and copper (II) oxide? Copper (II) oxide does give oxygen to zinc to oxidise it. The copper (II) oxide is said to be an oxidising agent as it results in the oxidation process. Therefore it is evident to refer the zinc as the reacting agent as it reduces the copper (II) oxide by removing oxygen.

In other words, a substance that can cause oxidation is an oxidising reaction(self-explanatory from the name, I guess).
The opposite is definitely true too, which means that a substance that can cause reduction is a reducing agent(also self-explanatory from the name).

Oxidation and reduction is also described as the loss and gain of hydrogen respectively of a substance.
An example of this would be hydrogen sulfide plus chlorine....
H2S(g) + Cl2 (g) --->2HCl(g) + S(s)

This reaction has shown the hydrogen sulfide to lose hydrogen, hence it is oxidised. The chlorine gas has gained the hydrogen and resulted in the reduction of chlorine. The chlorine has caused the oxidation of the hydrogen sulfide, hence being the oxidising agent..

However, this was not the only few definitions for oxidation and reduction!!
Oxidation is regarded as the loss of electrons of a substance, and reduction is seen as the direct opposite of it--the gain of electrons by a substance.This was when chemists were able to use the knowledge acquired through atomic structure to include reactions with the exclusion of O2 and H2.

A simple example of this kind of equation is the common reaction of sodium metal with chlorine gas---that's right our sodium chloride!:)

2Na(s) + Cl2(g) -->2NaCl

Electrons are transferred from the sodium atoms to the chlorine atoms to form sodium ions and chloride ions via a vice versa process. The chlorine gains electrons, so it is reduced. The Na loses electrons, hence being oxidised. The chlorine gains electrons, so it is reduced.