What is an oxidising agent and a reducing agent? Explain with examples.

(N/A) An oxidising agent is a substance that gains electrons and undergoes reduction in a chemical reaction. Conversely,a reducing agent is a substance that loses electrons and undergoes oxidation.
Consider the following redox reactions:
$2 Na_{(s)} + Cl_{2_{(g)}} \rightarrow 2 Na^{+} Cl_{(s)}^{-}$
$2 Na_{(s)} + S_{(s)} \rightarrow (Na^{+})_{2} S_{(s)}^{-2}$
$2 Na_{(s)} + \frac{1}{2} O_{2_{(g)}} \rightarrow (Na^{+})_{2} O_{(s)}^{-2}$
In these reactions,$Na$ loses electrons and is oxidized,acting as a reducing agent. $Cl_{2}$,$S$,and $O_{2}$ gain electrons and are reduced,acting as oxidising agents.
For example,the reaction between $Na$ and $Cl_{2}$ can be split into two half-reactions:
Oxidation half-reaction: $2 Na_{(s)} \rightarrow 2 Na^{+}_{(g)} + 2 e^{-}$
Reduction half-reaction: $Cl_{2_{(g)}} + 2 e^{-} \rightarrow 2 Cl^{-}_{(g)}$
Overall reaction: $2 Na_{(s)} + Cl_{2_{(g)}} \rightarrow 2 NaCl_{(s)}$
$A$ redox reaction is a process involving the transfer of electrons from one reactant to another.