(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.
                 

(iv) On counting and balancing atoms on both the sides, we get the balanced equation.