H₂S Solution S²⁻ Concentration

An aqueous solution contains 0.10 M H₂S and 0.20 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:

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