Arrange the following compounds in the descending order of their melting points

a)       n-pentane

b)      iso pentane

c)       neopentane

The decreasing order of melting points is: n-pentane > Iso pentane>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 melting point goes on decreasing.