Which reaction is useful for the exchange of halogen in alkyl chloride by iodide?

An alkyl bromide $(X)$ reacts with sodium in ether to form $4,5-$diethyl octane. The compound $X$ is:

In an $S_N1$ reaction on chiral centres,there is

Arrange the following in order of $C-Br$ bond strength in a polar solvent. The structures are as follows:
$(I)$ $1$-methylcyclohexa-$2,4$-dienyl bromide
$(II)$ cyclohexa-$2,4$-dienyl bromide
$(III)$ $1$-methylcyclopenta-$2,4$-dienyl bromide
$(IV)$ cyclopenta-$2,4$-dienyl bromide

Vicinal and geminal dihalides can be distinguished by using:

Which is the correct reactivity order for $E_2$ reaction with alcoholic $KOH$?