What is half - life of a reaction ? Illustrate your answer with an example.

The time during which the concentration of a reactant is reduced to one half of its initial concentration is called of half - life $\left({\mathrm{t}}_{(1/2)}\right)$ of the reaction.
Ex: ${\mathrm{t}}_{1/2}{\text{ of }}^{14}\mathrm{C}$ is 5730 years. It means that in 5730 years, ${ }^{14}\mathrm{C}$ is said to be reduced to half of its initial concentration.