(N/A) Alkanes experience intermolecular Van der Waals forces. The stronger the force,the higher the boiling point of the alkane.
As branching increases,the surface area of the molecule decreases,which results in a smaller area of contact between molecules.
Consequently,the Van der Waals forces decrease,which can be overcome at a relatively lower temperature. Hence,the boiling point of an alkane chain decreases with an increase in branching.
For example,consider the isomers of pentane $(C_5H_{12})$:
$1$. $n$-pentane (straight chain): Highest surface area,strongest Van der Waals forces,highest boiling point $(309.1 \ K)$.
$2$. iso-pentane ($2$-methylbutane): One branch,lower surface area,lower boiling point $(301.0 \ K)$.
$3$. neo-pentane ($2$,$2$-dimethylpropane): Two branches,spherical shape,smallest surface area,lowest boiling point $(282.5 \ K)$.
Therefore,the order of boiling point is: $n$-pentane $>$ iso-pentane $>$ neo-pentane.