You must have seen tarnished copper vessels being cleaned with lemon or tamarind juice. Explain why these sour substances are effective in cleaning the vessels.

Explanation

Coper metal slowly reacts with water, carbon dioxide and oxygen present in air to form basic copper carbonate which is green in colour. Its layer slowly gets deposited on the surface of the metal.
`2Cu + H_(2)O + underset("Present in air")(CO_(2)) + O_(2) to underset("Basic copper carbonate (green)")(Cu(OH)_(2)*CuCO_(3))`
Now as lemon is acidic, hence when we rub the tarnished copper vessel with lemon, the basic copper oxide or copper carbonate reacts with the acid present in lemon to form a salt which is washed away with water.