Question

Boiling point of petrol is
1.Below 20° C
2.170-120°C
3.35-70°C
4.270-340°C

Answer 1

Hint: Petrol or crude oil contains thousands of different compounds; boil over a temperature range as opposed to having a single point for a pure compound. The boiling point of hydrocarbons depends on carbon number, molecular size, and the type of hydrocarbons (aliphatic, naphthenic, or aromatic). It also depends on intermolecular forces

Step by step answer:

We should know that physical properties of hydrocarbons like alkanes all depend on the forces between the molecules - the intermolecular forces (intermolecular bonding). These are the weak attractive forces between the individual molecules.
The intermolecular bonds are much weaker than the covalent bonds, so when the hydrocarbon molecules have enough kinetic energy, it is the intermolecular forces which are overcome on vaporisation and the molecules stays intact.
If we have a more viscous liquid (sticky, less runny) then we can say that intermolecular attractive forces are higher between molecules because the liquid have series of molecules of similar structure. The more strongly the hydrocarbon molecules are attracted to each other, the less easily they run over each other, so the liquid itself does not flow as easily - not as fluid.
The molecule has a higher boiling point as more particle kinetic energy is needed to overcome the increasing intermolecular forces between the liquid molecules. The intermolecular forces increase between the hydrocarbon molecules increases as they get bigger (longer carbon chain)
Now if we asked about the boiling point of petrol we should first know that petrol is made of different alkanes that is pentane ( ) to heptane (). the molecule is less flammable as they become less volatile (less easily vaporised), again due to increasing intermolecular forces with increasing size of molecule so if we have, petrol which is composed of small molecules is much more flammable than lubricating oil that has bigger molecules and long carbon chains.
In petrol the intermolecular forces are great enough to raise the boiling point of it to above room temperature.
So by above points, now we can consider that option C as our correct answer.
Note:
Boiling point depends on atmospheric pressure. If we increase the pressure the more energy required for liquids to boil, and boiling point will be higher.
Higher Atmospheric Pressure = More Energy Required to Boil = Higher Boiling Point