Answer
Carbon dioxide has a higher boiling point than carbon monoxide because it has higher molecular mass.
CO is a weak dipole while $CO_{2}$ is a strong dipole. So, $CO_{2}$ can be more easily polarized than CO.
Work Step by Step
Carbon dioxide has a higher boiling point than carbon monoxide because it has higher molecular mass.
BP of Carbon dioxide = -78.5°C
BP of Carbon monoxide = -191°C
Molar mass of Carbon dioxide = 44
Molar mass of Carbon monoxide = 28
CO is a weak dipole while $CO_{2}$ is a strong dipole. So, $CO_{2}$ can be more easily polarized than CO.
