How many possible isomers of the compound having molecular formula $C_5{H}_{11}Br ?$

Molecular formula of the compound indicates that the compound is saturated and it has 5 carbon atoms, 11 hydrogen atoms and only one Br atoms. There are eight possible isomers:

1-bromopentane:

${\mathrm{CH}}_3-{\mathrm{CH}}_2-{\mathrm{CH}}_2-{\mathrm{CH}}_2-{\mathrm{CH}}_2-\mathrm{Br}$

2-bromopentane:

${\mathrm{CH}}_3-{\mathrm{CH}}_2-{\mathrm{CH}}_2-\mathrm{CH}\left(\mathrm{Br}\right)-{\mathrm{CH}}_3$

3-bromopentane:

${\mathrm{CH}}_3-{\mathrm{CH}}_2-\mathrm{CH}\left(\mathrm{Br}\right)-{\mathrm{CH}}_2-{\mathrm{CH}}_3$

1-bromo-2-methylbutane

${\mathrm{CH}}_3-{\mathrm{CH}}_2-\mathrm{CH}\left({\mathrm{CH}}_3\right)-{\mathrm{CH}}_2-\mathrm{Br}$

2-bromo-2-methylbutane:

${\mathrm{CH}}_3-{\mathrm{CH}}_2-\mathrm{C}\left({\mathrm{CH}}_3\right)\left(\mathrm{Br}\right)-{\mathrm{CH}}_3$

2-bromo-3-methylbutane:

${\mathrm{CH}}_3-\mathrm{CH}\left({\mathrm{CH}}_3\right)-\mathrm{CH}\left(\mathrm{Br}\right)-{\mathrm{CH}}_3$

1-bromo-3-methylbutane:

${\mathrm{CH}}_3-\mathrm{CH}\left({\mathrm{CH}}_3\right)-{\mathrm{CH}}_2-{\mathrm{CH}}_2-\mathrm{Br}$

1-bromo-2,2-dimethylpropane.

${\mathrm{CH}}_3-\mathrm{C}{\left({\mathrm{CH}}_3\right)}_2-{\mathrm{CH}}_2-\mathrm{Br}$