Question

which chemical is a dull green coating over copper vessels ?​

Answer 1

When a copper statue (or copper vessel) is exposed to moist air for long, it acquires a dull green coating. The green material is a mixture of copper hydroxide [Cu(OH)2] and copper carbonate (CuC03) formed due to the reaction of copper with moist air.

Answer 2

Answer -

When a copper vessel is exposed to moist air for a long time it develops a green layer on its surface. Copper corrodes by oxidation in which it reacts with oxygen in the air to form copper oxide. Copper oxide then combines with carbon dioxide to make copper carbonate, which gives it a green colour.