(a) Give reasons:
(i) H₃PO₃ undergoes disproportionation reaction but H₃PO₄ does not.
(ii) When reacts with excess of F₂, ClF₃ is formed not FCl₃.
(iii) Dioxygen is a gas while Sulphur is a solid at room temperature.
b. Write the structures of the following:
(i) XeF₄
(ii) HClO₃

OR

(a) When concentrated sulphuric acid was added to an unknown salt present in a test tube a brown gas (A) is evolved. This gas intensified when copper turnings were added to the 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 (A) change into solid while cooking?

(b) Arrange the following in the decreasing order of their reducing character :
HF, HCl, HBr, HI
c. Complete the following reaction:
${\mathrm{XeF}}_4+{\mathrm{SbF}}_5---->$