${{\mathrm{K}}_{\mathrm{\alpha }}}_1, {\mathrm{K}}_{{\mathrm{a}}_2} \mathrm{and} {\mathrm{K}}_{{\mathrm{a}}_3}$are the respective ionisation constants for the following reactions.

${\mathrm{H}}_2\mathrm{S}\rightleftharpoons {\mathrm{H}}^{+}+ {\mathrm{HS}}^{-}$ 

${\mathrm{HS}}^{-}\rightleftharpoons {\mathrm{H}}^{+}+ {\mathrm{S}}^{2-}$

${\mathrm{H}}_2\mathrm{S}\rightleftharpoons 2{\mathrm{H}}^{+}+ {\mathrm{S}}^{2-}$

The correct relationship between ${{\mathrm{K}}_{\mathrm{\alpha }}}_1, {\mathrm{K}}_{{\mathrm{a}}_2} \mathrm{and} {\mathrm{K}}_{{\mathrm{a}}_3}$ is

• A

  ${{\mathrm{K}}_{\mathrm{\alpha }}}_3 = {\mathrm{K}}_{{\mathrm{a}}_1} \times {\mathrm{K}}_{{\mathrm{a}}_2}$

• B

  ${{\mathrm{K}}_{\mathrm{\alpha }}}_3 = {\mathrm{K}}_{{\mathrm{a}}_1} + {\mathrm{K}}_{{\mathrm{a}}_2}$

• C

  ${{\mathrm{K}}_{\mathrm{\alpha }}}_3 = {\mathrm{K}}_{{\mathrm{a}}_1} - {\mathrm{K}}_{{\mathrm{a}}_2}$

• D

  ${{\mathrm{K}}_{\mathrm{\alpha }}}_3 = {\mathrm{K}}_{{\mathrm{a}}_1} / {\mathrm{K}}_{{\mathrm{a}}_2}$