Define pyrolysis.

Hint: Pyrolysis is a process of generating energy from waste materials. It involves the thermal decomposition of the organic material when an external source of energy is applied.

Complete step by step answer:
Pyrolysis is the process of thermal decomposition of a substance in a non-reactive atmosphere at high temperature. Here an external source of heat is applied to maintain the temperature in the range of ${\text{300 - 85}}{{\text{0}}^{\text{o}}}{\text{C}}$ for household and commercial wastes. The output from the pyrolysis process is a solid residue and a synthetic gas known as Syngas. Syngas contains a number of gases which are either combustible or non-combustible, this includes ${\text{Carbon Monoxide}}$,${\text{Hydrogen}}$,${\text{Methane}}$ and other volatile organic carbon containing compounds. Pyrolysis can be used to degrade fossil fuels based chemicals. The process of pyrolysis is irreversible. Pyrolysis process is used for the conversion of organic materials into solid materials containing ash, carbon and some small amount of liquids and gases.

Additional information: In pyrolysis pyro refers to fire and lysis refers to breakdown.
On pyrolysis we can convert the organic material into solid, liquid or gas. In case of solid, charcoal is formed and the process of formation of solid material from organic substance on applying a particular temperature in the absence of oxygen is called slow pyrolysis. If the material is converted into liquid, biofuel is obtained and this process is called as flash pyrolysis and if the material is converted into gas, fuel gas is obtained and this process is called as fast pyrolysis

Note:
Pyrolysis is used to produce charcoal, activated carbon, to convert biomass to biochar and also used to convert waste products into disposable substances in a chemical industry. The synthetic gas that is obtained during pyrolysis is used to produce electricity in steam turbines.