Explanation:

It is an ideal black body that absorbs all incident electromagnetic waves or radiation, regardless of the angle of incidence or frequency. As it absorbs all colours of light, it is named as black “body”.

• When the radiations are made to pass through a black body, it undergoes multiple reflections and is completely absorbed. When it is placed in a temperature bath of fixed temperature, the heat radiations will come out.

• Black absorbs heat, whereas white reflects heat. Therefore, black radiators retain heat better and keep you warmer than white radiators. Yherefore it is a good radiator.

• The radiation emitted by the blackbody is known as blackbody radiation. In order to stay in thermal equilibrium, a black body must emit radiation at the same rate as it absorbs, and so it must also be a good emitter of radiation.

Hence option 3rd is correct,