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Halides form an ionic compound with metals due to the electronegativity difference between the halide and the metal. The ionic character and stability of the bond increase with the increase in electronegativity difference between the atoms.

For metals showing varying oxidation states, the most stable halide formed depends on the oxidizing power of the halide ion. Their size and electronegativity can determine the oxidizing power of the halogens.

The process of adding oxygen or removing electrons causing an increase in oxidation state is called oxidation. An oxidizing agent is a substance that can help in the oxidation of another species by accepting electrons.

An oxidizing agent gets reduced during the process. The extent to which a substance can carry out the oxidation of another species is called its oxidizing power and depends on the electronic structure of its atom.

The oxidizing power of halogens can be identified from the oxidation states of rhenium ions in the compounds formed by each halogen.

The oxidation state of rhenium is +6 in$ReC{l}_6$ , +5 in $ReB{r}_5$, and +4 in$Re{I}_4$ . Therefore, chlorine can oxidize rhenium into a +6 oxidation state; bromine can oxidize rhenium to a +5 oxidation state, and iodine can oxidize rhenium into a +4 oxidation state.

The oxidizing power is directly proportional to the extent of oxidation by the halide ion. Therefore, the halide ion that can produce the highest oxidation state in metal will have the highest oxidizing power.

Therefore, the order of oxidizing power can be shown as

$C{l}_2>B{r}_2>I_2$