The melting points of n-pentane (I), isopentane (II) and neopentane (III) increase in the order.

No. of carbon atoms increases mp / Bp increases.

 The decreasing order of boiling points is:
n-pentane>Isopentane>Neopentane
or


This is because, with the increase in branching, the surface area decreases. As a result of it, the magnitude of van der Waal's forces of attraction decreases, and therefore boiling point goes on decreasing.