Which of the following alkenes is the most stable?

Which alkene on ozonolysis gives $CH_3CH_2CHO$ and $CH_3COCH_3$?

Addition of $BH_3$ followed by $H_2O_2$ to $trans-2-butene$ would give a product which is

Surprisingly,the reaction shown below goes through a classical carbocation. What is the major product of this reaction?

$CH_3-CH=CH_2$ $\xrightarrow[reagent]{\text{Bayer's}} X$ $\xrightarrow{HIO_4} \text{product},$
Product is

What will be the product in the following reaction?
(Image of methylenecyclohexane reacting with $NBS$)