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

$17 \, mg$ 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 $...........$.

The reaction of propene with $Cl_2$ at $400-600\,^oC$ gives...........

The reaction of ethene with $Cl_2$ in a saturated solution of $KBr$ yields:

The compound most likely to decolourize a solution of potassium permanganate is

In the given reaction
$CH_3CH_2CH=CHCH_3$ $\xrightarrow{X}$ $CH_3CH_2COOH + CH_3COOH$
The $X$ is