'X' melts at low temperature and is a bad conductor of electricity in both liquid and solid state. X is :

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 :

White Phosphorus on reaction with concentrated NaOH solution in an inert atmosphere of CO₂ gives phosphine and compound (X). (X) on acidification with HCl gives compound (Y). The basicity of compound (Y) is :

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 :