Q. Assertion (A) In the species, each of two extreme bromine exhibits oxidation state of and the middle bromine of .
Reason (R) The average of three oxidation numbers of bromine of the is .

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Solution:

The structure of (tribromooctaoxide) is
image
Thus, oxidation state of two corner atoms is and of middle one is . The difference in oxidation states is due to difference in bonding situations.
Average oxidation state
Thus, both and are correct but is not the correct explanation of .