Which of the following,when added to a solution of acetic acid,will decrease the concentration of hydrogen ions?

In the precipitation of the iron group $(III)$ in qualitative analysis,ammonium chloride is added before adding ammonium hydroxide to :

Calculate $[S^{2-}]$ and $[HS^{-}]$ of the solution which contains $0.1 \ M \ H_2S$ and $0.3 \ M \ HCl$.
[$K_{a1} = 1.0 \times 10^{-7}$ and $K_{a2} = 1.3 \times 10^{-13}$ for $H_2S$]

The solubility of $AgCl$ is least in which of the following solutions?

Given below are two statements:
Statement $I$: On passing $HCl_{(g)}$ through a saturated solution of $BaCl_2$,at room temperature white turbidity appears.
Statement $II$: When $HCl$ gas is passed through a saturated solution of $NaCl$,sodium chloride is precipitated due to common ion effect.
In the light of the above statements,choose the most appropriate answer from the options given below:

The solubility (in $mol \ L^{-1}$) of $AgCl$ $(K_{sp} = 1.0 \times 10^{-10})$ in a $0.1 \ M \ KCl$ solution will be