Q.Nitrogen forms a number of oxides and oxoacids.

Among the given oxides, N2O is neutral; nitric acid is made in the lab from a nitrate salt and conc. H2SO4, and is a strong oxidising acid with wide industrial uses.

1. Neutral oxide of nitrogen Nitrogen forms several oxides that are acidic (N2O3, N2O5), mixed acidic (NO2, N2O4, which give a mixture of acids with water), and neutral (NO, N2O - these do not react with water/alkali to form acids/salts). Of the given choices, N2O (i) is the neutral oxide (N2O5 is strongly acidic - the anhydride of HNO3; NO2 and N2O4 are mixed acid anhydrides).
2. Nitric acid - laboratory preparation, properties, uses Laboratory preparation: HNO3 is prepared by heating a nitrate salt (KNO3 or NaNO3) with concentrated sulphuric acid in a glass retort at a moderate temperature (~450 K), since HNO3 is volatile and distils off as it forms: NaNO3 + H2SO4 -> NaHSO4 + HNO3 (heat) The HNO3 vapour is condensed and collected. Chemical properties:

1. Strong monobasic acid - fully ionises in water to give H3O+ and NO3-.
2. Strong oxidising agent - it oxidises most metals (except noble metals like Au, Pt) and several non-metals. With concentrated HNO3 it is reduced to NO2 (brown gas); with dilute HNO3 it is usually reduced to NO: Cu + 4HNO3 (conc.) -> Cu(NO3)2 + 2NO2 + 2H2O 3Cu + 8HNO3 (dilute) -> 3Cu(NO3)2 + 2NO + 4H2O
3. Passivation - concentrated HNO3 renders Fe, Co, Al and Cr passive by forming a thin protective oxide layer on their surface, so they resist further attack.
4. Oxidises non-metals - e.g. carbon and sulphur are oxidised to CO2 and H2SO4 respectively with hot concentrated HNO3.
5. Brown ring test - HNO3/nitrates give a characteristic brown ring with freshly prepared FeSO4 solution and concentrated H2SO4, used to confirm nitrate ion. …