If all the nucleophilic substitution reactions at saturated carbon atoms in the above sequence of reactions follow $S_N2$ mechanism, then $\underline{E}$ and $\underline{E}$ will be respectively,

Among the bromides $(I)-(III)$ given below,the order of reactivity for ${S_N}^1$ reaction is:

Which of the following reagents,when heated with ethyl chloride,forms ethylene?

When $3-$methylbutan$-2-$ol is treated with $HBr$,the following reaction takes place:
$CH_3-CH(CH_3)-CH(OH)-CH_3 \xrightarrow{HBr} CH_3-C(Br)(CH_3)-CH_2-CH_3$
Give a mechanism for this reaction.
(Hint : The secondary carbocation formed in step $II$ rearranges to a more stable tertiary carbocation by a hydride ion shift from $3^{rd}$ carbon atom.)

Which among the following is $NOT$ a feature of $S_{N}2$ mechanism?

The major product obtained on treatment of $CH_3CH_2CH(F)CH_3$ with $CH_3O^-/CH_3OH$ is