With increase in molecular mass boiling point increases. Thus the b.p. of pentan-1-ol will be more than other given compounds. Now, among isomeric alcohols $1^{\circ}$ alcohols have higher boiling points than $2^{\circ}$ alcohols due to higher surface area in $1^{\circ}$ alcohols.
Hence, increasing order of b.p. will be
Propan-1-ol $ < $ butan-2-ol $ < $ butan-1-ol $ < $ pentan-1-ol.