On heating, lead (II) nitrate gives a brown gas (A). The gas (A) on cooling changes to a colourless solid/liquid (B). (B) on heating with NO changes to a blue solid (C). The oxidation number of nitrogen in solid (C) is :

In a molecule of pyrophosphoric acid, the number of P - OH, P = O and P - O - P bonds/moiety(ies) respectively are :

Aqua regia is used for dissolving noble metals (Au, Pt, etc.). The gas evolved in this process is :

On heating compound (A) gives a gas (B) which is a constituent of air. This gas when treated with H₂ in the presence of a catalyst gives another gas (C) which is basic in nature. (A) should not be :