Explanation

(b)
Possible isomers are as follows :
$CH_{3}$ $CH_{3}$
$|$ $|$
$CH_{3}CH_{2}CH_{2}CH_{2}OH$ $CH_{3}CHCH_{2}OH$, $CH_{3} - C - OH$
(I) (II) $|$
$CH_{3}$
(III)
$CH_{3} - CH - CH_{2} - CH_{3}$
$|$
$OH$
(IV)
Here, only (I), (II) and (III) are chain isomers