In the dehydrohalogenation of $2$-bromobutane,which conformation leads to the formation of $cis$-but-$2$-ene?

Bottles containing $C_6H_5I$ and $C_6H_5CH_2I$ lost their original labels. They were labelled $A$ and $B$ for testing. $A$ and $B$ were separately taken in test tubes and boiled with $NaOH$ solution. The end solution in each tube was made acidic with dilute $HNO_3$ and then some $AgNO_3$ solution was added. Substance $B$ gave a yellow precipitate. Which one of the following statements is true for this experiment?

In nucleophilic aliphatic substitution,the nucleophiles are generally

Predict the product of the following reaction:
(Image: $A$ chiral carbon attached to a phenyl ring with a para-chloro group,a deuterium atom $(D)$,a hydrogen atom $(H)$,and a chlorine atom (Cl) in a specific stereochemical configuration. The reaction is with $NaI$ in acetone.)

The following order can be correct for:
$F^{-} > Cl^{-} > Br^{-} > I^{-}$

Which of the following is an incorrect statement?