BHU PMT BHU PMT (Screening) Solved Paper-2008

  • question_answer
    In the reduction of\[KMn{{O}_{4}}\]by warm acidified oxalic acid, the oxidation number of Mn changes from

    A)  + 4 to + 2            

    B)  + 6 to + 4

    C)  + 7 to +2             

    D)  + 7 to + 4

    Correct Answer: C

    Solution :

                     \[[MnO_{4}^{-}+8{{H}^{+}}+5{{e}^{-}}\xrightarrow{{}}M{{n}^{2+}}+4{{H}_{2}}O]\times 2\] \[\begin{align}   & \underline{\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,[{{C}_{2}}o_{4}^{2-}\xrightarrow{{}}2C{{O}_{2}}+2{{e}^{-}}]\times 5} \\  & \underline{\begin{align}   & 2MnO_{4}^{-}+5{{C}_{2}}O_{4}^{2-}+16{{H}^{+}}\xrightarrow{{}}2M{{n}^{2+}} \\  & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,+10C{{O}_{2}}+8{{H}_{2}}O \\ \end{align}} \\ \end{align}\] So, oxidation number of Mn changes in the above reaction from + 7 to + 2.


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