Describe the preparation and an analytical use of ${\mathrm{I}}_2{\mathrm{O}}_5$.

Explain why solid ${\mathrm{CsI}}_3$ is stable but solid ${\mathrm{NaI}}_3$ is not.

Draw the shapes of the following molecules and ions, showing the positions of the lone pairs of electrons:

$\mathrm{ClF}, {\mathrm{BrF}}_3, {\mathrm{IF}}_5, {\mathrm{IF}}_7, {\mathrm{I}}_3^{-}, {\mathrm{ICl}}_4^{-}$ and ${\mathrm{I}}_5^{-}$