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

The solubility of $AgI$ in $NaI$ solution is less than that in pure water because

If acetic acid is mixed with sodium acetate,then the ${H^{+}}$ ion concentration will be:

What concentration of $Ac^{-}$ ions will reduce $H_3O^{+}$ ion concentration to $2 \times 10^{-4} \ M$ in a $0.40 \ M$ solution of $HAc$ (in $M$)? Given $K_a (HAc) = 1.8 \times 10^{-5}$.

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 of $BaSO_4$ in pure water is $10^{-5} \ M$ at $298 \ K$. The solubility of $BaSO_4$ in $0.1 \ M \ K_2SO_4$ (aq.) solution is: (Molar mass of $BaSO_4 = 233 \ g \ mol^{-1}$)