The conjugate base of H2S (hydrogen sulfide) is HS− (bisulfide or hydrosulfide ion).
To understand this, let’s first clarify what a conjugate base is. When an acid donates a proton (H+), it turns into its conjugate base. In the case of H2S, it can lose one proton to form HS−. This means that HS− is the species that remains after H2S donates a proton.
Furthermore, HS− can also act as an acid and donate a proton to form S2− (sulfide ion), illustrating how conjugate acid-base pairs work. Thus, H2S is an acid, and HS− is its conjugate base.