Question

The oxoanion in which the oxidation state of the central atom is not as same as its group number in the periodic table is:

• A. ${VO}_2^{-}$
• B. ${MnO}_4^{2-}$
• C. ${Cr}_2{O}_7^{2-}$
• D. none of these

Answer 1

The correct option is A ${VO}_2^{-}$

(A)In $V{O}_2^{-}$ ion, the oxidation state of vanadium is +3. Vanadium belongs to group 5 or (VB).
Hence, option B is correct
(B) In permanganate ion $\left({MnO}_4^{2-}\right)$, the oxidation state of manganese is +7. Manganese belongs to group 7 or (VIIB)
Hence, option C is incorrect.
(C) In dichromate ion ${Cr}_2{O}_7^{2-}$, the oxidation number of chromium is +6. Chromium belongs to group 6 or (VIB).
Hence, option D is incorrect.