K_a1, K_a2 and K_a3 are the respective ionisation constants for the following reactions

H₂ S ⇋ H⁺ + HS^-

HS ⇋ H⁺ + S^2-

H₂S ⇋ 2H⁺ + S^2-

The correct relationship between K_a1 , K_a2 and K_a3 is

For the reaction : H₂ S ⇋ H⁺ + HS^-

the ionization constant -

(i)

^o For the reaction : HS ⇋ H⁺ + S^2-

the ionization constant -

(iii)

From this two above reaction, we can get the following reaction (addition)

H₂S ⇋ 2H⁺ + S^2-

Then Ka₁ and Ka₂ will also be added and Ka₃ will be the result :

From equation (i) and (ii) x (here addition means the multiplication of the Equilibrium constants)