Place these hydrocarbons in order of decreasing boiling point:
paraffin, c40h82,
propane, c3h8,
heptane, c7h16,
triptane, c7h16(also known as 2,2,3-trimethylbutane), and
hexadecane, c16h34.

The given compounds are alkanes. This means that the formula is C_nH_2n+2

The general trend for boiling point in alkanes is that the greater number of carbon atoms, the higher the boiling point. If the alkane is branched, the branched alkane will have a higher boiling point than the straight chain.

Taking these into account: propane < heptane < triptane < hexadecane < paraffin 

tracks, burrows, eggshells, nests, tooth marks, or gastroliths

the ideal gas law equation is as follows

pv = nrt

where p - pressure

v - volume

n - number of moles

r - universal gas constant

t - temperature

so if the pressure, volume and temperature are already known

we are left with n and r

since r is the universal gas constant that has a known fixed value then r too is known

so we are left with 'n'

once we know temperature volume and pressure

we can find the number of moles of gas present using the ideal gas law equation

this is not my own answer, this is an answer for the same question by the user blahblahmali. i do not claim ownership of this account.