Which of the following compounds has the highest boiling point. 2pentanone, pentanol, pentane, and pentanal

            1-Pentanol has the highest boiling point.

Explanation:
                   Boiling points of given compounds are as follow,

                 1) 2-Pentanone  =  101 °C

                 2) 1-Pentanol  =  138 °C

                 3)  Pentane  =  36.1 °C

                 4)  Pentanal  =  103 °C

Pentanol has greatest boiling point as compare to others because it involes a strongest intermolecular interactions called as hydrogen bond interactions. Remaining compounds lack the direct attachement of hydrogen to most electrnegative atom like oxygen which is present in 1-Pentanol.