Explain why lower alkanes are gaseous in state and higher alkanes are liquid in state?

(N/A) Alkanes are non-polar molecules held together by weak van der Waals forces.
The strength of these van der Waals forces increases with the increase in molecular size and surface area as the number of carbon atoms increases.
For lower alkanes ($C_{1}$ to $C_{4}$),the molecular mass is small,and the van der Waals forces are too weak to hold the molecules together in a liquid or solid state at room temperature $(298 \ K)$,hence they exist as gases.
As the number of carbon atoms increases ($C_{5}$ to $C_{17}$),the molecular mass and surface area increase,leading to stronger van der Waals forces,which are sufficient to hold the molecules together in the liquid state at room temperature.