Account for the following: (i) Ozone is thermodynamically unstable. (ii) Solid $\mathrm{PCl}_5$ is ionic in nature. (iii) Fluorine forms only one oxoacid HOF. (b) Draw the structure of (i) $\mathrm{BrF}_5$ (ii) $\mathrm{XeF}_4$ OR (i) Compare the oxidising action of $\mathrm{F}_2$ and $\mathrm{Cl}_2$ by considering parameters such as bond dissociation enthalpy, electron gain enthalpy and hydration enthalpy.(ii) Write the conditions to maximize the yield of $\mathrm{H}_2\mathrm{SO}_4$ by contact process.(iii) Arrange the following in the increasing order of property mentioned :(a) $\mathrm{H}_3\mathrm{PO}_3, \;\; \mathrm{H}_3\mathrm{PO}_4, \;\; \mathrm{H}_3\mathrm{PO}_2 \;\;$ (Reducing character).(b) $\mathrm{NH}_3, \;\; \mathrm{PH}_3, \;\; \mathrm{AsH}_3, \;\; \mathrm{SbH}_3, \;\; \mathrm{BiH}_3$ (Base strength).