71.Which of the following statements are true ? 1. Teflon and dacron are polymers. 2. Neoprene is synthetic rubber. 3. Polythene is polyethylene polymer. 4. Natural rubber is chloroprene.

72.Which of the following statements about a refrigerator is/are correct ? 1. It converts electrical energy into heat energy. 2. It converts electrical energy into mechanical energy. 3. It transfers heat from a high temperature to a low temperature. 4. It transfers heat from a low temperature to a high temperature.

73.AC cannot be used in

74.Rectifiers are used to convert

75.A substance which changes readily into vapour without heating is called