An aqueous solution contains 0.10 M H2S and 0.20 M HCl. If the equilibrium constants for the formation of HS– from H2S is 1.0 × 10–7 and that of S2– from HS–ions is 1.2×10–13 then the concentration of S2– ions in aqueous solution is :
(1) 3×10–20
(2) 6×10–21
(3) 5×10–19
(4) 5×10–8