Question

If copper is kept exposed to damp air for a considerable time, it gets a green coating on its surface. This is due to the formation of ______.

Options

• hydrated copper sulphate

• copper oxide

• basic copper carbonate

• copper nitrate

Answer 1

If copper is kept exposed to damp air for a considerable time, it gets a green coating on its surface. This is due to the formation of basic copper carbonate.

Explanation:

When copper is exposed to damp air for a long time, it slowly undergoes corrosion by reacting with atmospheric carbon dioxide, oxygen, and water vapour. This chemical reaction forms a green layer on its surface, which is a basic mixture of copper carbonate and copper hydroxide [CuCO₃.Cu(OH)₂]. The other options are incorrect because copper oxide is black or brown, while copper sulphate and copper nitrate typically form blue or blue-green crystals under different laboratory conditions, rather than a natural corrosion patina.