The preferred reagent for the preparation of pure alkyl chloride from alcohol is

The reaction of allyl alcohol with $MCPBA$ ($meta$-chloroperbenzoic acid) is shown below:
Allyl alcohol $\xrightarrow{MCPBA}$ Product
What is the stereochemistry of the product of the above reaction?

Consider the following reaction:
$CH_3CH_2OH$ $\xrightarrow{PBr_3} X$ $\xrightarrow{alc. KOH} Y$ $\xrightarrow[(ii) H_2O, \text{heat}]{(i) H_2SO_4, \text{room temperature}} Z$
The product $Z$ is

Which of the following is a tertiary alcohol?

What is the decreasing order of reactivity of $HX$ in the reaction $ROH + HX \to RX + H_2O$?

Product $(C)$ is