Arrange the halogens ${\mathrm{F}}_2, {\mathrm{Cl}}_2, {\mathrm{Br}}_2, {\mathrm{I}}_2$, in order of their increasing reactivity with alkanes.

The addition of $\mathrm{HBr}$ to But-$1$-ene gives a mixture of products $\mathrm{A}, \mathrm{B}$ and $\mathrm{C}$

$\left(\mathrm{C}\right) {\mathrm{CH}}_3– {\mathrm{CH}}_2–{\mathrm{CH}}_2–{\mathrm{CH}}_2–\mathrm{Br}$
The mixture consists of

Arrange the following carbanions in order of their decreasing stability.

$\left(\mathrm{A}\right) {\mathrm{H}}_3\mathrm{C}-\mathrm{C}\equiv {\mathrm{C}}^{-} \left(\mathrm{B}\right) \mathrm{H}-\mathrm{C}\equiv {\mathrm{C}}^{-} \left(\mathrm{C}\right) {\mathrm{H}}_3\mathrm{C}-{{\mathrm{CH}}_2}^{-}$

Arrange the following alkyl halides in decreasing order of the rate of $\mathrm{\beta }$-elimination reaction with alcoholic $\mathrm{KOH}$.