Question

The colour of the sky is black in absence of atmosphere.Give reason

Answer 1

because in the absence of atmosphere things do not emit light and when there is no light then it is black. that's why the colour of sky is black in the absence of atmosphere..

Answer 2

Without the atmosphere there is nothing local to act as a (secondary) source of light, so there is no light and we conventionally call objects that emit (little or) no light "black". So the non-object that is "the sky" could be called "black".

Hope it helps