A metal (A) on heating in nitrogen gas gives compound B. B on treatment with H₂O gives a colourless gas which when passed through CuSO₄ solution gives a dark blue-violet coloured solution. A and B respectively, are :

The number of bonds between sulphur and oxygen atoms in S₂O₈^2- and the number of bonds between sulphur and sulphur atoms in rhombic sulphur, respectively, are :

In the following reaction, products (A) and (B) respectively, are :

NaOH + Cl₂ $$ \to $$ (A) + side products
(hot and conc.)

Ca(OH)₂ + Cl₂ $$ \to $$ (B) + side products (dry)

The C–C bond length is maximum in :