Column - I	Column - II
A) K	1) Oxidising agent
B) Br	2) Oxidation
C) ${\text{Na}}^{+}+{\text{e}}^{-}\to \text{Na}$	3) Reduction
D) $2\text{C}{l}^{-}\to \text{C}{l}_2+2{\text{e}}^{-}$	4) Reducing agent

Oxidation: Loss of electrons by an atom or ion. Ex: $2\text{C}{l}^{-}\to \text{C}{l}_2+2{\text{e}}^{-}$

Reduction: Gain of electrons by an atom or ion. Ex: ${\text{Na}}^{+}+{\text{e}}^{-}\to \text{Na}$

Oxidizing agent: The species which undergoes reduction and oxidize others.         

Ex: Non-metals like Br, Cl, F

Reducing agent: The species which undergoes oxidation and reduces others.

Ex: Metals like Na, Mg, K.