n-Butanol and 2-methyl propanol are a pair of which isomers

${\mathrm{CH}}_3{\mathrm{CH}}_2{\mathrm{CH}}_2{\mathrm{CH}}_2\mathrm{OH} ; {\mathrm{CH}}_3-\stackrel{\stackrel{\mathrm{H}}{|}}{\underset{\underset{{\mathrm{CH}}_3}{|}}{\mathrm{C}}}-{\mathrm{CH}}_2\mathrm{OH}$

n-Butanol ;      2-methyl propanal

                       2-methyl - 1 propanol

  Both are chain isomers.