Hydrogen sulphide (H2S) is a strong reducig agent. Which of the following reactions shows its reducing action

(a) Cd(NO3)2+ H2S --------- CdS+ 2HNO​3

(b) CuSO4+ H2S ------------ CuS + H2SO4

(c) 2FeCl3+ H2S ------------ 2FeCl2+ 2HCl + S

(d) Pb(NO3)2 + H2S ---------- PbS + 2CH3COOH

The third reaction shows the reducing action of hydrogen sulphide. That means it reduces the given salt and that itself get oxidised. 
 2FeCl3+ H2S 2FeCl2+ 2HCl + SFeCl3Oxidation state of Fex+3(-1) = 0x= +3FeCl2Oxidation state of Fex+2(-1) = 0x= +2Thus iron gets reduced from +  3 to +2At the sametime H2S gets oxidised to SH2S2(1) + x =0x =-2In the rightsideS=0Thus S oxidation state changes from -2 to 0

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