Answer:
Correct option is (a).
Explanation:
Solubility equilibrium of ZnS is represented as-
[tex]ZnS\rightleftharpoons Zn^{2+}+S^{2-}[/tex]
[tex]S^{2-}[/tex] is a strong conjugate base of weak acid [tex]H_{2}S[/tex].
Therefore addition of HCl in ZnS results formation of [tex]H_{2}S[/tex]. Thus [tex]S^{2-}[/tex] is removed as [tex]H_{2}S[/tex].
[tex]S^{2-}+2H^{+}\rightleftharpoons H_{2}S[/tex]
So, ZnS tends to be more soluble with addition of dilute HCl to keep constant solubility product.