Balance the following equation by oxidation number method.
(i) The skeleton equation along with oxidation number of each atom is
     +3 -1   +1 -2    +2-1   +1-1  0
     FeCl3  + H2S   FeCl2 + HCl + S
     (Fe = +3) (S = 2) (Fe = +2) (S =0)
(ii) Noting the change on O. N. of above atoms
Increase     S = -2 to  0 i.e.  2
Decrease     Fe = +3  to +2 i.e. 1
(iii) Equalise the increase/decrease in O.N. by multiplying FeCl3 by 2.
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(iv) On counting and balancing atoms on both the sides, we get the balanced equation.
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Balance the following chemical equation by oxidation number method:
       in acidic medium.