The addition of $HCl$ will not suppress the ionization of

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

Statement $A$: Addition of $NH_4OH$ in the presence of excess $NH_4Cl$ to an aqueous solution of $BaCl_2$ results in the precipitation of $Ba(OH)_2$.
Reason $R$: $Ba(OH)_2$ is insoluble in water.

Pure $NaCl$ is prepared by passing $HCl$ gas through a saturated solution of common salt in water. The principle used is:

If $S_1, S_2, S_3$ and $S_4$ are the solubilities of $AgCl$ in water,in $0.01 \ M \ CaCl_2$,in $0.01 \ M \ NaCl$ and in $0.05 \ M \ AgNO_3$ respectively at a certain temperature,the correct order of solubilities is

Consider the following equilibrium: $AgCl_{(s)} + 2NH_{3(aq)} \rightleftharpoons [Ag(NH_3)_2]^+_{(aq)} + Cl^-_{(aq)}$. $A$ white precipitate of $AgCl$ appears on adding which of the following?