Question

The general formula of mono halogen derivatives of alkane is:
(A) ${{\text{C}}_n}{{\text{H}}_{n + 1}}{\text{X}}$
(B) ${{\text{C}}_n}{{\text{H}}_{2n}}{\text{X}}$
(C) ${{\text{C}}_n}{{\text{H}}_{2n - 1}}{\text{X}}$
(D) ${{\text{C}}_n}{{\text{H}}_{2n + 1}}{\text{X}}$

Answer 1

To obtain general formula of mono halogen derivatives of alkanes, remove one hydrogen atom from the general formula of alkanes and add one halogen atom. The general formula of alkanes is ${{\text{C}}_n}{{\text{H}}_{2n + 2}}$ .

Complete answer:
The general formula of alkane is ${{\text{C}}_n}{{\text{H}}_{2n + 2}}$:
The examples of alkanes include methane $\left( {{\text{C}}{{\text{H}}_4}} \right)$ , ethane $\left( {{{\text{C}}_2}{{\text{H}}_6}} \right)$ propane $\left( {{{\text{C}}_3}{{\text{H}}_8}} \right)$ butane $\left( {{{\text{C}}_4}{{\text{H}}_{10}}} \right)$ and so on. When one hydrogen atom of alkanes is replaced with a halogen atom, mono halogen derivatives are obtained. The examples of mono halogen derivatives of alkanes include methyl chloride $\left( {{\text{C}}{{\text{H}}_3}{\text{Cl}}} \right)$ , ethyl chloride $\left( {{{\text{C}}_2}{{\text{H}}_5}{\text{Cl}}} \right)$ propyl chloride $\left( {{{\text{C}}_3}{{\text{H}}_7}{\text{Cl}}} \right)$ butyl chloride $\left( {{{\text{C}}_4}{{\text{H}}_9}{\text{Cl}}} \right)$ and so on.
The general formula of mono halogen derivatives of alkane is ${{\text{C}}_n}{{\text{H}}_{2n + 1}}{\text{X}}$:

Hence, the correct option is the option (D).

Additional Information: The general formula ${{\text{C}}_n}{{\text{H}}_{2n - 1}}{\text{X}}$ represents mono halogen derivatives of alkenes. When a hydrogen atom of alkene is replaced with a halogen atom, the mono halogen derivative with general formula ${{\text{C}}_n}{{\text{H}}_{2n - 1}}{\text{X}}$ is obtained. The examples of mono halogen derivatives of alkanes include ${\text{C}}{{\text{H}}_2}{\text{ = CHCl, C}}{{\text{H}}_3}{\text{CH = CHCl, C}}{{\text{H}}_3}{\text{C}}{{\text{H}}_2}{\text{CH = CHCl, C}}{{\text{H}}_3}{\text{C}}{{\text{H}}_2}{\text{C}}{{\text{H}}_2}{\text{CH = CHCl }}$
and so on. The examples of corresponding alkenes are ${\text{C}}{{\text{H}}_2}{\text{ = C}}{{\text{H}}_2}{\text{, C}}{{\text{H}}_3}{\text{CH = C}}{{\text{H}}_2}{\text{, C}}{{\text{H}}_3}{\text{C}}{{\text{H}}_2}{\text{CH = $CH_2$, C}}{{\text{H}}_3}{\text{C}}{{\text{H}}_2}{\text{C}}{{\text{H}}_2}{\text{CH = C}}{{\text{H}}_2}$.

Note: Mono halogen derivatives of alkanes are called alkyl halides. Here, halogen atoms can be either fluorine, chlorine, bromine or iodine. In addition to mono halogen derivatives, there are di, tri, tetra and poly halogen derivatives of alkanes. Mono, di, tri, tetra and poly halogen derivatives of alkanes contain one, two, three, four and several halogen atoms. In poly halo derivatives of alkanes, the halogens can be of the same element or of different elements. Thus, for example, one molecule of poly halogen derivative might contain one chlorine, two bromine and one iodine atom.