Q.When copper is heated with conc. HNO3 it produces

Nitric acid (HNO3) is prepared in the laboratory by heating potassium or sodium nitrate with concentrated sulphuric acid (KNO3 + H2SO4 -> KHSO4 + HNO3) at a carefully controlled low temperature to limit its own decomposition. Industrially it is made by Ostwald's process: ammonia (from the Haber process) is catalytically oxidised over platinum gauze at ~1275 K to nitric oxide (4NH3 + 5O2 -> 4NO + 6H2O), which is further air-oxidised to nitrogen dioxide (2NO + O2 -> 2NO2) and absorbed in water in a series of towers to give the acid (3NO2 + H2O -> 2HNO3 + NO, with the NO recycled).

Pure nitric acid is a colourless liquid (b.p. 86 °C) that forms a constant-boiling 98% azeotrope with water; it decomposes on standing/in light (4HNO3 -> 4NO2 + 2H2O + O2), which is why the concentrated acid yellows on storage. Nitric acid is unusual in acting simultaneously as an acid, an oxidising agent and (with H2SO4) a nitrating agent. As an acid it neutralises bases/basic oxides normally; as an oxidant it converts non-metals (C, S, P, I2) to their oxoacids/oxides while itself being reduced (typically to NO2 or NO), and it renders metals like Al, Fe, Cr passive by forming a protective oxide film, so it essentially never liberates H2 gas from a metal. Its reaction with metals proceeds through a primary step (forming the metal nitrate and releasing nascent hydrogen), a secondary step (this hydrogen reducing more HNO3 to NO2/NO/N2O/NH2OH/NH3 de …