The dissociation of a weaker acid can be suppressed or stopped by the addition of stronger acids which is known as common ion effect
Let's check about group || reagents
[tex]\\ \rm\rightarrowtail H_2S\longrightarrow H^++S^{2-}[/tex]
[tex]\\ \rm\rightarrowtail HCl \longrightarrow H^++Cl^-[/tex]
Here Hydrogen sulphide is neutralized by a stronger acid HCl
