Give the increasing order of stability for the following alkenes based on their heat of hydrogenation $(\Delta H^o)$:
$(I) (CH_3)_2C = C(CH_3)_2$
$(II) CH_3CH_2CH_2CH = CH_2$
$(III) (CH_3)_2C = CHCH_3$
$(IV) CH_3CH_2C(CH_3) = CH_2$

Given below are two statements: one is labelled as Assertion $(A)$ and the other is labelled as Reason $(R)$.
Assertion $(A)$: Cis form of alkene is found to be more polar than the trans form.
Reason $(R)$: Dipole moment of trans isomer of $2$-butene is zero.
In the light of the above statements,choose the correct answer from the options given below:

An alkene $X$ $(C_6H_{12})$ on ozonolysis gives acetaldehyde and ethyl methyl ketone. What is the product formed when $X$ reacts with $HBr$?

Which of the following is formed when propene is heated with chlorine at high temperature?

The major product of the above reaction is

Which of the following reactions proceeds via a secondary free radical?