Correct Answer - D
Boiling point of alkanes increases with increase in molecular mass and for the same alkane the boiling point decreases with branching.
Thus, the decreasing order of their boiling points is:
`underset(III)("n-Pentane") gt underset((II))("2-Methylbutane")gt underset((IV))("2,2-Dimethylpropane")gtunderset((I))("n-Butane")`