In which of the following reactions does an acid-base reaction take place?

How many bond cleavages are required to convert cubane into a non-cyclic skeleton?

Which of the following most accurately describes the first step in the reaction of hydrogen chloride with $1$-butene?

What is the acid $(A)$ obtained in the following reaction sequence?
${C_2H_5I}$ $\xrightarrow{\text{alc. KOH}} X$ $\xrightarrow[CCl_4]{Br_2} Y$ $\xrightarrow{KCN} Z$ $\xrightarrow{H_3O^+} A$

Action of hydrogen chloride on $CH_3-C(CH_3)=CH_2$ and on $CH \equiv CH$ will predominantly give the compounds,respectively

$A$ molecule $P$ on treatment with acid undergoes rearrangement and gives $Q$. $Q$ on ozonolysis followed by reflux under alkaline condition gives $R$. The structure of $R$ is given below:
[Image of $R$]
The structure of $P$ is