The correct option is A 2.0
At equilibrium
2H2S(s)⇌2H2(g)+S2(g) At equi. (0.1−x) x x2
conc. (0.1−x)0.4 x0.4 x0.8
Equilibrium constant,
Kc=[H2]2[S2][H2S]2
putting the values,
Kc=[x0.4]2[x0.8][(0.1−x)0.4]2
or x30.8(0.1−x)2=1.0×10−6
Now, as x is very small
⇒0.1−x→0.1
⇒x=2×10−3
So, percent dissociation =2×10−30.1×100=2.0