Assertion :You must have seen tarnished copper vessels being cleaned with lemon or tamarind juice. Reason: Copper reacts with moist carbon dioxide in air to form copper carbonate and as a result, copper vessel loses its shiny brown surface forming a green layer of copper carbonate. Tarnished copper vessels are cleaned with lemon or tamarind juice to give the surface of the copper vessel its charateristic lustre.

The correct option is A Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
Tarnished copper vessels are being cleaned with lemon or tamarind because copper vessel forms a basic layer of copper oxide which is greenish in color and it is cleaned by lemon. Lemon is citric acid and have the power to clean copper by dissolving this copper oxide tarnish. The tarnish dissolves into the acid and is washed away. The acidic nature of lemon removes the oxidation on the copper vessel.