The isomerism not exhibited by the compound with molecular formula ${\mathrm{C}}_4{\mathrm{H}}_9\mathrm{Br}$ is

(1)  ${\mathrm{CH}}_3{\mathrm{CH}}_2{\mathrm{CH}}_2{\mathrm{CH}}_2\mathrm{Br}$   (2)  ${\mathrm{CH}}_3{\mathrm{CHBrCH}}_2{\mathrm{CH}}_3$
(3)   ${\left({\mathrm{CH}}_3\right)}_2{\mathrm{CHCH}}_2\mathrm{Br}$      (4)  ${\left({\mathrm{CH}}_3\right)}_3\mathrm{CBr}$
(1) & (2) ……. Positional
(1) & (3) ……. Chain
(1) & (4) ……. Chain
(2) & (3) ……. Chain
(3) & (4) ……. Positional

$2^0$ butyl bromide shows optical isomer

 Geometrical isomerism is not  possible.