Arrange the following sets of compounds in order of their increasing boiling points:
(a) Pentan-1-ol, butan-1-ol, butan-2-ol, ethanol, propan-1-ol, methanol.
(b) Pentan-1-ol, n-butane, pentanal, ethoxyethane.

Explanation

(a) Boiling points increase regularly as the molecular mass increases due to the corresponding increase in their van der waals forces of attraction. Thus, boiling points increase in the order:
methanol, ethanol, propan-1-ol, butan-1-ol and pentan-1-ol.
Among isomeric alcohols, `2^(@)` alcohols have lower boiling points than `1^(@)` alcohols due to a corresponding decrease in the extent of H-bonding because of steric hindrance. thus, the b.p. of butan-2-ol is lower methanolltethanolltpropan-1-olltbutan-2-olltbutan-1-olltpentan-1-ol
(b) Boiling points of ethers having molecular mass equal to or less than n-butane (i.e., 58 g `mol^(-1)`) are higher than those of the corresponding n-alkanes. however, the boiling points of ethers having molecular mass equal to or higher than n-pentane (i.e., 72 g `mol^(-1)`) are lower than the corresponding n-alkanes . thus, b.p. of n-butane is lower than that of ethoxyethane. further, the b.ps of alcohols are much higher than those of alkanes, and ethers of comparable molecular masses due to intermoleclar H-bonding. however, b.ps of aldehydes are lower than those of corresponding alcohols due to absence of H-bonding but are still higher than those of alkanes and ethers of comparable molecular mass. thus, the overall increasing order of b.ps is n-butanltethoxyethaneltpentanalltpentan-1-ol.