The position isomer of isobutyl alcohol is

[Step 1]:

Isobutyl alcohol is $\underset{3}{\mathrm{C}}{\mathrm{H}}_3-\underset{2}{\overset{\stackrel{{\mathrm{CH}}_3}{|}}{\mathrm{C}}}\mathrm{H}-\underset{1}{\mathrm{C}}{\mathrm{H}}_2-\mathrm{OH}$

(1)  ${\mathrm{CH}}_3-{\mathrm{CH}}_2-\underset{\underset{\mathrm{OH}}{|}}{\mathrm{CH}}-{\mathrm{CH}}_3$
(2)  ${\mathrm{CH}}_3-{\mathrm{CH}}_2-{\mathrm{CH}}_2-{\mathrm{CH}}_2-\mathrm{OH}$
(3)  $\underset{3}{\mathrm{C}}{\mathrm{H}}_3-\underset{\underset{\mathrm{OH}}{|}}{\overset{\stackrel{{\mathrm{CH}}_3}{|}}{{}_2\mathrm{C}}}-\underset{1}{\mathrm{C}}{\mathrm{H}}_3$
Compounds having the same molecular formula but different in position of  substituents (or) functional groups.
Therefore 2-Methyl-2-propanol is functional isomer of isobutyl alcohol.
Isobutyl alcohol is