(a) Give reasons:
(i) ${\mathrm{H}}_3{\mathrm{PO}}_3$ undergoes disproportionation reaction but ${\mathrm{H}}_3{\mathrm{PO}}_4$ does not.
(ii) When ${\mathrm{Cl}}_2$ reacts with excess of ${\mathrm{F}}_2,{\mathrm{ClF}}_3$ is formed and not ${\mathrm{FCl}}_3$.
(iii) Dioxygen is a gas while sulphur is a solid at room temperature.
(b) Draw the structures of the following:
(i) ${\mathrm{XeF}}_4$
(ii) ${\mathrm{HClO}}_3$
OR
(a) When concentrated sulphuric acid was added to an unknown salt present in a test tube, a brown gas (A) was evolved. This gas intensified when copper turnings were added to this test tube. On cooling, the gas (A) changed into a colourless solid (B).
(i) Identify (A) and (B).
(ii) Write the structures of (A) and (B).
(iii) Why does gas (A) change to solid on cooling ?
(b) Arrange the following in the decreasing order of their reducing character :
$\mathrm{HF},\mathrm{H},\mathrm{HBr},\mathrm{HI}$
(c) Complete the following reaction:
${\mathrm{XeF}}_4+{\mathrm{SbF}}_5\to$