(i) Freon 12:- the chlorofluorocarbon compounds of methane and ethane are collectively known as freons. They are extremely stable,unreactive, non-toxic and non-corrosive. Example of Freon 12 is CCl₂F₂. It is mainly used in refrigeration and eventually makes its way into the atmosphere where it diffuses unchanged into the stratosphere. In stratosphere, Freon is able to initiate the radical chain reactions that can upset the natural ozone balance.

(ii) DDT: - it stands for p, p’-Dichlorodiphenyltrichloroethane (DDT). It is mainly used as an insecticide.

(iii) Iodoform: - it was earlier used as an antiseptic but the antiseptic properties are due the liberation of free iodine and not due to the iodoform itself. Due to its objectionable smell, it has been replaced by other formulations containing iodine.

(iv) Carbon tetrachloride (CCl₄):- it is used as an industrial solvent for oils, fats, resins etc. and also in dry cleaning. Used as a cleaning fluid both in industries, as a degreasing agent and in the home, as a spot remover and as a fire extinguisher.