Normal straight-chain , branched, and cyclic alkanes are all types of alkanes, which are hydrocarbons containing only single covalent bonds between carbon and hydrogen atoms. The difference in their boiling points is primarily due to their molecular structure and the strength of the intermolecular forces acting between the molecules.1. Normal straight-chain alkanes: These alkanes have a linear arrangement of carbon atoms, with hydrogen atoms bonded to them. The boiling points of normal alkanes generally increase with increasing molecular weight, as the strength of the London dispersion forces a type of van der Waals force increases with the size of the molecule.Example: n-pentane C5H12 has a boiling point of 36.1C 97F .2. Branched alkanes: These alkanes have one or more carbon atoms bonded to more than two other carbon atoms, creating a branching structure. Branched alkanes generally have lower boiling points than their straight-chain isomers because their compact structure reduces the surface area available for intermolecular interactions, leading to weaker London dispersion forces.Example: 2-methylbutane C5H12 is an isomer of n-pentane and has a boiling point of 27.9C 82.2F .3. Cyclic alkanes: These alkanes have a closed-ring structure, with carbon atoms bonded to form a cycle. Cyclic alkanes generally have higher boiling points than their straight-chain counterparts due to the presence of stronger London dispersion forces and, in some cases, ring strain. The increased rigidity of the cyclic structure can also lead to stronger intermolecular interactions.Example: cyclopentane C5H10 has a boiling point of 49.3C 120.7F .In summary, the boiling points of alkanes vary depending on their molecular structure. Normal alkanes generally have higher boiling points than branched alkanes due to their larger surface area and stronger London dispersion forces, while cyclic alkanes typically have even higher boiling points due to their rigid structure and stronger intermolecular interactions.