Salt S on heating with copper turning and sulphuric acid liberates a reddish brown gas.identify the anion S

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Solution

The reddish brown gas is Nitrogen dioxide (NO₂) and is formed from the nitrate salt on heating with copper turnings and sulphuric acid. First the sulphuric acid reacts with nitrate salts to form nitric acid which then reacts with copper to liberate nitrogen dioxide which is brown in colour.
Cu + 4 HNO₃ -------> Cu(NO₃)₂ + 2H₂O + 2NO₂

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