The boiling point of alkanes increases with an increase in molecular mass (number of carbon atoms) due to stronger van der Waals forces . For isomeric alkanes, the boiling point decreases with an increase in branching because the molecule becomes more spherical, reducing the surface area of contact and the magnitude of intermolecular forces .

Therefore, the order of boiling points based on the number of carbon atoms and branching is:

1. Heptane (7 carbons)
2. Hexane (6 carbons)
3. 2-Methylbutane (5 carbons)
4. Butane (4 carbons, unbranched)
5. 2-Methylpropane (4 carbons, branched).

This corresponds to the sequence (a) > (e) > (c) > (b) > (d).