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.

(N/A) Copper reacts with moist carbon dioxide in the air to form copper carbonate,which results in the copper vessel losing its shiny brown surface and forming a green layer of copper carbonate.
The citric acid present in lemon or tamarind juice neutralizes the basic copper carbonate and dissolves the layer.
This is why tarnished copper vessels are cleaned with lemon or tamarind juice to restore the characteristic lustre of the copper surface.