The bond angle between $C-O$ and $O-H$ bonds in alcohols is close to (in $^{\circ}$)

Among the given compounds,the correct dehydration order is:

$HO-CH_2CH_2CH_2CH_2-Br \xrightarrow{KOH} \text{Product}$. The product is:

An alcohol $X$ $(C_5H_{12}O)$ on dehydration gives $Y$ (major product). Reaction of $Y$ with $HBr$ gave $Z$ ($C_5H_{11}Br$,major product). $Z$ undergoes nucleophilic substitution in two steps. What are $X$ and $Y$?

The product formed in the following multistep reaction is:

Which of the following alcohols reacts most rapidly with hydrogen halides?