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 vessels lose their 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 characteristic lustre.
A.Both assertion and reason are correct and reason is the correct explanation for assertion
B.Both assertion and reason are correct but reason is not the correct explanation for assertion.
C.Assertion is correct but reason is incorrect
D.Both assertion and reason are incorrect

Hint:Copper vessels undergo corrosion on exposure to carbon dioxide in air forming basic copper carbonate and copper oxide. Lemon and tamarind juice are acidic in nature.

Complete step by step solution:
The corrosion of copper is known as tarnishing which refers to change in colour since copper reacts with oxygen and carbon dioxide in air to form black colored layer of copper oxide and a green colored layer of copper carbonate. Both these compounds are basic in nature.
Lemon juice is acidic in nature due to the presence of citric acid. When rubbed on the surface of the tarnished copper vessels, it reacts with the basic copper oxide and copper carbonate. Since it is a neutralization reaction, a salt is formed which can then be removed by washing the vessel with water. Thus the colored tarnish is removed and thus, the original color and lustre of the copper vessel is retained.
Similarly, tamarind juice is acidic as well due to presence of tartaric acid and performs a similar mechanism to clean the tarnished copper vessels.
From the above statements we can say, that both the assertion and the reason are correct statements with the reason being the correct explanation for the assertion.

Thus, the correct option is A.

Note:
Corrosion can be defined as the degradation of metals because of an electrochemical process, namely oxygen. Various examples of corrosion are the rusting of iron, black tarnish on silver and development of blue-green platina on the surface of copper. The corrosion of copper can be prevented by using some sort of a grease on its surface that forms a protective layer between the copper surface and the atmospheric gases.