Petrol = it is a liquid which is used as a fuel for motor vehicles.

• There is a choice of petrol and diesel engines.
• The car was fully supplied with petrol and water.
• We had to stop at the next petrol station.
• petrol fumes/tank.

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Patrol = ( especially of soldiers or the police) to go around an area or a building to see if there is any trouble or danger.

• The soldiers on patrol duty.
• The whole area is patrolled by the CRPF because of the possibility of riots.
• The police found a deserted car while on patrol after midnight.
• Security guards are posted to patrol the folklore museum consequent to the threat from militants.

Note:- Petrol- the stress is at the first syllable.;  Patrol – the stress is at the second syllable.