Correct Option: C

when concentrated hydrosulphuric acid is added to dry potassium nitrate brown fumes are evolved and these fumes are evolved due to the formation of nitrogen dioxide. Nitrogen dioxide is the chemical compound with the formula NO2. It is one of several nitrogen oxides. NO2 is an intermediate in the industrial synthesis of nitric acid, millions of tons of which are produced each year. This reddish-brown toxic gas has a characteristic sharp, biting odour and is a prominent air pollutant. Nitrogen dioxide is a paramagnetic and bent molecule.