Butane, ch3ch2ch2ch3, has a higher boiling point than propane, ch3ch2ch3. this is due to:

Explanation:

Boiling point - the temperature at which the the vapor pressure of the liquid equals the external atmospheric pressure.

From the question,

Butane and propane have different number of carbon atoms ,

Now to convert the liquid to gas , energy in the form of heat is provided , now to melt butane more amount of energy is required , due to more number of atoms present in butane , more energy is required and hence , butane has more boiling point .

In comparison to butane , propane has lesser atoms and hence , require less energy to convert liquid propane to gaseous propane , and therefore has less boiling point.

it is the most commonly accepted one