KEAM 2014 Physics and Chemistry Paper

Permanganate ion is MnO4−
(i) Conversion of permanganate into manganese (II) salt.
MnO4−⟶Mn2+
x+(−2)4=−1+2
x+7
Change in number of electrons =7−2=5
(ii) Conversion of permanganate into manganate
MnO4−⟶MnO42−
x+(−2)4=−1x+(−2)4=−2
  x=+7      x=+6
Change in number of electron =7−6=1
(iii) Conversion of permanganate into manganese dioxide (MnO2)
MnO4−⟶Mn2+O2
x+(−2)4=−1  x+(−2)2=0
   x=+7   x−4=0
         x=+4
Change in number of electrons =7−4=3 Thus, the number of electrons involved in the given reduction processes are respectively 5,1,3