Different hydrogen atoms in the compound $CH_3-CH=CH-CH_2-CH_2-CH(CH_3)_2$ are represented by alphabets $A, B, C, D, E, F$. Arrange them in decreasing order of reactivity towards free radical substitution.

Among the following free radical bromination reactions,select those in which a $2^o$ halide is the major product. The reactions are as follows:
$(P)$ Cyclohexane + $Br_2/hv$
$(Q)$ Methylcyclobutane + $Br_2/hv$
$(R)$ Ethylbenzene + $Br_2/hv$
$(S)$ $3-$Methylhexane + $Br_2/hv$
$(T)$ Decalin + $Br_2/hv$
$(U)$ Butane + $Br_2/hv$

$A$ compound reacts with $Cl_2$ to give product $(B)$,and the reaction of product $(B)$ with $(Zn + \text{dilute } HCl)$ gives back the original substance $(A)$. Give the structures of $(A)$ and $(B)$.

Which of the following alkanes is used for road surfacing?

The major product formed in the following reaction is:
$CH_3-CH(CH_3)-CH_3 \xrightarrow[CH_3OH]{CH_3OBr}$

Which of the following is the most reactive alkane?