What are the enthalpies of $\sigma$-bond and $\pi$-bonds in an alkene?

Arrange the following compounds in the decreasing order of their reactivity towards electrophilic addition of $HBr$:
$(a)$ $CH_3-C(CH_3)=CH_2$
$(b)$ $CH_3O-C(CH_3)=CH_2$
$(c)$ $CH_3OCH_2-C(CH_3)=CH_2$

An unknown alkene $(A)$ reacts with $3 \ mole$ of $H_2$ gas in the presence of a platinum catalyst to form $1$-isopropyl-$4$-methylcyclohexane. When the unknown alkene $(A)$ is ozonized and reduced,the following products are obtained:
$HCHO$,$OHC-CH_2-CO-CO-CH_3$,and $CH_3-CO-CH_2-CHO$
What is the structure of alkene $(A)$?

Identify the major product $A$ in the following reaction.
$3-$Bromo$-2-$methylpentane $\xrightarrow{alc. KOH} A$

Propane is obtained from propene by which method?

An alkyl bromide produces a single alkene when it reacts with sodium ethoxide and ethanol. This alkene undergoes hydrogenation and produces $2-$methylbutane. What is the identity of the alkyl bromide?