Sounds travels most rapidly in solid objects, especially those that are dense. These objects have closely packed atoms, and energy that is traveling in vibrations (the sound) can easily pass between the touching atoms.
It has to be a metal, it can't be anything else.
<span>Since these molecules are all non-polar, the only intermolecular force of attraction will be London dispersion forces. Since these increase by the size of the molecule, the boiling points will decrease in the same order:
Parafin > Heptadecane > hexane > 2,2-dimethylbutane > propane
For these two, hexane > 2,2-dimethylbutane, dispersion forces are greater in a molecule which is longer and unbranched compared to one which is branched and more compact.</span>
