The tetraethyl lead mixed with petrol works as

1. Cooling agent
2. Anti – knocking agent
3. Bleaching agent
4. None of the above

It works as anti-knocking agent.“Tetraethyl lead” was used in early model cars to help reduce engine knocking, boost octane ratings, and help with wear and tear on valve seats within the motor.In modern car engines, the petrol vapour-air mixture is highly compressed before it is sparked, in order to get the maximum energy from the burning fuel. However, some hydrocarbons tend to ignite under pressure before they are sparked, so that the engine runs roughly; this is known as "knocking".