UPSC CDS 1 2020 GK Paper

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Question : 23 of 120

Marks: +1, -0

Silver articles become black after some time when exposed to air because

silver gets oxidized to silver oxide
silver reacts with moist carbon dioxide in the air to form silver carbonate
silver reacts with sulphur in the air to form a coating of silver sulphide
silver reacts with nitrogen oxides in the air to form silver nitrate

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