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

Identify '$X$' and '$Y$' in the following sequence of transformations: $CH_3-CH_2-CH_2Br$ $\xrightarrow{X} \text{Product}$ $\xrightarrow{Y} CH_3-CH(Br)-CH_3$.

What is the major product formed when $3$-phenylpropene reacts with $HBr$?

In the reaction shown,the major product obtained is:

Two bottles containing $C_6H_5I$ and $C_6H_5CH_2I$ have lost their original labels. They are labeled as $A$ and $B$ for testing. $A$ and $B$ are taken separately in test tubes and boiled with $NaOH$ solution. The final solution of each test tube is acidified with dilute $HNO_3$ and a little $AgNO_3$ is added. Solution $B$ gives a yellow precipitate. Which of the following statements is correct?

The reactivity of ethyl chloride towards nucleophilic substitution is: