Question

Assertion: A greenish layer appears on copper vessels, if left uncleaned.
Reason: It is due to the formation of a layer of basic copper carbonate.
Read both the assertion and reason and choose the correct option for it.
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.

Answer 1

Copper vessels tarnish in the air due to the aerial oxidation of the cu with the atmospheric oxygen leading to the formation of the layer on the surface of the copper and it can even result into corrosion if left exposed and uncovered for longer duration of time.

Complete answer:
The natural conversion of the metal into the more refined chemical form is known as corrosion; it is the gradual degradation of the material by the chemicals and oxygen of the air. A greenish layer appears on copper vessels, if left uncleaned. It is due to the formation of a layer of basic copper carbonate, this can be represented as:
$Cu(s) + C{O_2}(g) + {O_2}(g) + {H_2}O(l)\xrightarrow{{MoistAir}}C{u_2}C{O_3}.{(OH)_2}$
The copper carbonate $C{u_2}C{O_3}.{(OH)_2}$ formed is green in colour and is basic in nature.

Thus Both Assertion and Reason are correct and Reason is the correct explanation for Assertion and thus Option A is the correct answer.

Note:
The copper is usually immune to the corrosion it behaves like a Noble metal but under some conditions it gets corroded when left uncovered. The corrosion of Copper is called Patina.