The number of possible mono halogen derivatives for the molecular formula C₄H₁₀ (Excluding stereo isomers)

$$\begin{gathered} {\mathrm{CH}}_3 {\mathrm{CH}}_2 {\mathrm{CH}}_2- {\mathrm{CH}}_2-\mathrm{X} (1-\mathrm{Halo} \mathrm{butane}) \\ {\mathrm{CH}}_3 \mathrm{CH}\left({\mathrm{CH}}_3\right) - {\mathrm{CH}}_{2 }-\mathrm{X} (2 -\mathrm{Methyl} 1-\mathrm{Halo} \mathrm{butane}) \\ {\mathrm{CH}}_3- \mathrm{C}{\left({\mathrm{CH}}_3\right)}_2-\mathrm{X} (2,2-\mathrm{di} \mathrm{methyl} 1-\mathrm{Halo} \mathrm{propane}) \\ {\mathrm{CH}}_3 {\mathrm{CH}}_2 \mathrm{CHX}- {\mathrm{CH}}_3( 2-\mathrm{Halo} \mathrm{Butane}) \end{gathered}$$