Alkenes usually show which type of reaction?

What is the major product of the following reaction?

The olefin which on ozonolysis gives $CH_3CH_2CHO$ and $CH_3CHO$ is

Addition of $HBr$ to propene yields $2$-bromopropane,while in the presence of benzoyl peroxide,the same reaction yields $1$-bromopropane. Explain and give mechanism.

When $2-$Methylbut$-2-$ene is treated with hydrogen chloride,the major product obtained is

The product of the following reaction is: