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The trend of metallic properties is not that obvious in group 17. Fluorine is the most electronegative element and has no basic properties. Iodine and Bromine dissolve in oleum and other strong oxidising solvents forming species like [I2]+ and [Br2]+. Many other species like [I3]+ and [Br3]+ have also been prepared.
The bond length in [Br2]+ ion is 2.15 ∘A whereas the bond length of Br2 is 2.27 ∘A. This shows: