Ka1, Ka2 and Ka3 are the respective ionisation constants for the following reactions.

H2SH++HS-HS-H++S2-H2S2H++S2-

The correct relationship between Ka1, Ka2 and Ka3 is

(1) Ka3=Ka1×Ka2

(2) Ka3=Ka1+Ka2

(3) Ka3=Ka1-Ka2

(4) Ka3=Ka1/Ka2

(1) HINT: Use basic properties of equilibrium constant.
 
For the reaction,
H2SH++HS-Ka1=[H+][HS-][H2S]
For the reaction,
HS-H++S2-Ka2=[H+][S2-][HS-]
When, the above two reactions are added, their equilibrium constants are multiplied, thus
Ka3=[H+]2[S2-][H2S]=Ka1×Ka2
Hence, Ka3=Ka1×Ka2