What are $X$ and $Y$ in the following reaction?
Pent-$2$-ene $\xrightarrow[(ii) Zn / H_2O]{(i) O_3} X + Y$

$CH_3-C(CH_3)=CH-CH_3 \xrightarrow{Hg(OAc)_2/EtOH} (A) (90\%)$. The product $(A)$ of the above reaction is:

An alkene $A$ (molecular formula $C_{5}H_{10}$) on ozonolysis gives a mixture of two compounds $B$ and $C$. Compound $B$ gives a positive Fehling's test and also forms iodoform on treatment with $I_{2}$ and $NaOH$. Compound $C$ does not give Fehling's test but forms iodoform. Identify the compounds $A, B$ and $C$. Write the reaction for ozonolysis and the formation of iodoform from $B$ and $C$.

The major product of the following reaction is:

Which of the following has the most negative heat of hydrogenation?

The number of possible organobromine compounds which can be obtained in the allylic bromination of $but-1-ene$ with $N-bromosuccinimide$ $(NBS)$ is