$1$-methyl ethylene oxide (propylene oxide) when treated with an excess of $HBr$ produces:

Which alkyl halide from the following pairs would you expect to react more rapidly by an $S_N2$ mechanism? Explain your answer.
$(i)$ $CH_3CH_2CH_2CH_2Br$ or $CH_3CH_2CH(Br)CH_3$
$(ii)$ $CH_3CH_2CH(Br)CH_3$ or $(CH_3)_3CBr$
$(iii)$ $CH_3CH(CH_3)CH_2CH_2Br$ or $CH_3CH_2CH(CH_3)CH_2Br$

What do you mean by dehydrohalogenation?

The increasing order of densities of the following alkyl halides is:
$(I)$ $n-C_3H_7Br$
$(II)$ $n-C_3H_7Cl$
$(III)$ $n-C_3H_7I$

For the reactions given below:
$(I)$ Cyclohexyl chloride $\rightarrow$ Cyclohexyl cation + $Cl^-$,$\Delta H_1^{\circ}$
$(II)$ Cyclohex$-2-$enyl chloride $\rightarrow$ Cyclohex$-2-$enyl cation + $Cl^-$,$\Delta H_2^{\circ}$
$(III)$ Benzyl chloride $\rightarrow$ Benzyl cation + $Cl^-$,$\Delta H_3^{\circ}$
$(IV)$ Chlorobenzene $\rightarrow$ Phenyl cation + $Cl^-$,$\Delta H_4^{\circ}$
The correct decreasing order of enthalpies of reaction for producing the carbocation is:

Which of the following reagents is used in the preparation of nitroalkane from haloalkane?