Which of the following has the lowest boiling point?

Four C atom alkane, van der Waals forces of attraction are weak and boiling point is the lowest.As far as the boiling points are concerned, alkenes have more boiling point than alkanes with the same number of C atoms.Due to of the presence of rc-bond, alkenes are slightly polar. More is the number of n-bonds, more is the polarity and higher is the boiling point. Thus, the decreasing order of boiling points is:3>2>1>4.