Identify $X$ and $Y$ in the following reaction sequence: $X$ $\xrightarrow{Zn} Y$ $\xrightarrow[Zn, H_2O]{O_3} (CH_3)_2CO + CH_2O$

Assertion : $trans-2-Butene$ on reaction with $Br_2$ gives $meso-2,3-dibromobutane$.
Reason : The reaction involves $syn-addition$ of bromine.

Compound $X$ on reaction with $O_{3}$ followed by $Zn/H_{2}O$ gives formaldehyde and $2-$methylpropanal as products. The compound $X$ is :

What is the major product formed when $cis-2-butene$ reacts with $Br_2$ in $CCl_4$?

$17 \, mg$ of a hydrocarbon ($M$.$F$. $C_{10}H_{16}$) takes up $8.40 \, mL$ of $H_2$ gas measured at $0^{\circ}C$ and $760 \, mm$ of $Hg$. Ozonolysis of the same hydrocarbon yields acetone,formaldehyde,and a compound with the structure $CH_3-CO-CH_2-CH_2-CHO$. The number of double bonds present in the hydrocarbon is $...........$.

Arrange the following according to the increasing order of stability: Propene $(I)$,cis-but-$2$-ene $(II)$,trans-but-$2$-ene $(III)$,$2,3$-dimethylbut-$2$-ene $(IV)$,ethene $(V)$.