Propene on treatment with $HBr$ gives

Reagent $A$ may be:

Identify products $A$ and $B$ in the following reaction sequence:
$1$-methylcyclopentene $\xrightarrow{\text{dil. } KMnO_4, 273 \ K} A$ $\xrightarrow{CrO_3} B$

Reaction of $Br_2$ on ethylene in the presence of $NaCl$ gives:

Which among the following alkenes is most stable?

Which hydrogen in compound $(E)$ is easily replaceable during bromination reaction in the presence of light?
$CH_3 - CH_2 - CH = CH_2$
$(E)$