When metals like Zn and Cu react with concentrated nitric acid, nitrogen oxides are produced as by-products. The nature of the oxide depends on the metal's reactivity. Zinc (Zn), being more reactive, reacts with concentrated HNO to form nitrogen dioxide (NO ), a brown toxic gas. Copper (Cu), though less reactive, also forms NO with concentrated nitric acid. In both cases, NO is the nitrogen oxide formed due to the strong oxidizing nature of concentrated HNO . Thus, in both reactions, the nitrogen oxide evolved is NO .
