Which one has high rate of evaporation petrol or alcohol? Why?

Petrol as high rate of evaporation, because it is one of the fraction of hydrocarbons which is non -polar in nature.

Vander Waal forces are present in case of petrol which are of weak intermolecular forces of attraction so they are easily evaporated.

In case of alcohol, it is having the capability to form intermolecular hydrogen bonding which are stronger than the Vander Waal forces of attraction.

So, evaporation is slow when compared to that of petrol.

Alcohol

It depends on the particular sample of petrol, which can have a vapor pressure anywhere between 48.2 kPa to 103 kPa.

It also depends on what kind of alcohol. The vapor pressure of ethanol is 5.95 kPa.

So I'd expect petrol to evaporate more quickly.

As to "why", it's probably because the alcohol has more hydrogen bonds.