Question

copper does not burn but the hot metal is coated with a black colored layer of copper oxide. explain

Answer 1

At normal temperature, the surface of copper is covered withcopper oxide. The thin layer of copper oxide is a protective cover which protects copper from further oxidation. Thus this copper oxide does not burnas it is already reacted with the oxygen in the air.

Answer 2

This is because copper is active when hot. So when heated Cu is exposed to the atmosphere, it combines with atmospheric O2, forming CuO which as you said is black in colour.