Final answer:
Propane has the lowest boiling point among the given alkanes due to its smallest molecular mass which leads to weaker London dispersion forces compared to the other alkanes listed.
Step-by-step explanation:
The student asked which alkane has the lowest boiling point among octane, butane, ethane, hexane, and propane. The boiling points of alkanes are primarily influenced by the strength of the London dispersion forces, which increase with molecular mass and surface area. Since propane (C3H8) has the smallest molecular mass among the given alkanes, it has the weakest London dispersion forces and, consequently, the lowest boiling point.
Therefore, the order from lowest to highest boiling point for the hydrocarbons mentioned in the question is as follows: propane (-42.1°C) < ethane (C2H6) < butane (C4H10) < hexane (C6H14) < octane (C8H18).