Which of the following is least reactive towards $S_N2$ reaction?

Which of the following are correct statements about $C_2H_5Br$?

The major product $(A)$ formed in the reaction given below is:

Which of the following is most reactive towards nucleophilic substitution reaction?

The correct pair$(s)$ of the ambident nucleophiles is (are):
$(A)$ $AgCN / KCN$
$(B)$ $RCOOAg / RCOOK$
$(C)$ $AgNO_{2} / KNO_{2}$
$(D)$ $AgI / KI$

Among the following compounds $I-IV$,which one forms a yellow precipitate on reacting sequentially with $(i)$ $NaOH$,$(ii)$ dil. $HNO_{3}$,and $(iii)$ $AgNO_{3}$?