An energy efficient device for producing light is:
A. CFL
B. CNG
C. LPG
D. MCB

Hint: The above problem is based on the concept of energy efficient lighting device. There are many electric lighting devices like electric bulb, light emitting diode, CFL and tube light. Electric lighting is said to be energy efficient if it converts the maximum amount of input supply into light with minimum loss of supply as heat.

Complete step by step answer:
-The CFL is the electric lighting device that stands for compact fluorescent lamps. It uses the halogen gas to glow the electric lamp. The atoms of halogen gas produce light due to ionization. It converts maximum supply into light, so the CFL is an energy efficient device for producing light and the option (A) is the correct answer.
-The CNG is the gaseous fuel that stands for Compressed Natural Gas. It works as the fuel in automobile or other industrial processes. It is not used for lighting purposes, so the option (B) is incorrect.
-The LPG is the gaseous fuel that stands for Liquefied Natural Gas. It works as the fuel in domestic or other industrial processes. It is not used for lighting purposes, so the option (C) is incorrect.
-The MCB is an electric device that stands for Miniature Circuit Breaker. This electric device is used for protection against the electric shock of the circuit. The MCB is not used for the lighting purpose, so the option (D) is incorrect.

Hence, option (A) is the correct answer.

Note:The working and application of the entire lighting device is necessary for solving the above problem. The light emitting diode is the most efficient lighting device among the entire lighting devices at present.