Which of the following halogen oxides is ionic :
A. ${{I}_{4}}{{O}_{9}}$
B. ${{I}_{2}}{{O}_{5}}$
C. $Cl{{O}_{3}}$
D. $Br{{O}_{2}}$

Hint: Generally all the halogen oxides are covalent in nature. But in the case of iodine it generally exists in various oxidation states so, some oxides of iodine are ionic.

Complete Step by Step Answer:
${{I}_{4}}{{O}_{9}}$ is an ionic oxide as it is dissociated into tripositive iodine ions and its corresponding anion. Thus it is an ionic oxide.

It dissociate as follows:
${{I}_{4}}{{O}_{9}}\to {{I}^{3+}}+(I{{O}_{3}})_{3}^{-}$

All the other oxides that is ${{I}_{2}}{{O}_{5}}$, $Cl{{O}_{3}}$ and $Br{{O}_{2}}$have covalent bond so, these are covalent oxides.
Thus the correct option is A.

Additional Information: Iodine is a halogen element. It has the symbol of $I$. It generally exists as a gas. It has the colour of violet blue. Iodine is generally obtained from seaweed. Starch generally acts as an indicator in titration reactions to determine the end point of a titration. Iodine gas reacts with starch, an indicator gives blue colour. Iodine is a group $17$ elements. It has an atomic number of $56$. In the presence of starch it gives blue coloration.

Note: This ionic oxide of iodine that is $I_4O_9$ is called iodine nonooxide. It is a yellow colored solid compound. It undergoes thermal decomposition at high temprature. It is an unstable compound.