Copper becomes green when exposed to moist air for a long period. This is due to :

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the formation of a layer of cupric oxide on the surface of copper.

the formation of basic copper sulphate layer on the surface of the metal.

the formation of a layer of cupric hydroxide on the surface of copper.

the formation of a layer of basic carbonate of copper on the surface of copper.

answer is D.

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Detailed Solution

Copper becomes green when exposed to moist air for a long period. This is due to the formation of a layer of basic carbonate of copper on the surface of copper.

When copper metal is exposed to air, it becomes green due to corrosion. In the rainy season, when a copper vessel is exposed to air, the metal interacts with gases, moisture, and atmospheric gases to generate a combination of copper carbonate and copper hydroxide. This causes the surface of copper metal to become green.

The reaction is as follows:

$2 Cu + H_{2} O + {CO}_{2} + O_{2} \to Cu (OH)_{2} + {CuCO}_{3}$

As a result of the creation of a layer of basic carbonate of copper on the surface of copper when exposed to wet air for an extended length of time, copper becomes green.

Therefore, option D is correct.

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