The correct answer is A. Tetraethyl lead.
Tetraethyl lead (TEL) is a gasoline additive that was used to increase the octane rating of gasoline and reduce engine knocking. It is a toxic substance that is no longer used in gasoline due to environmental concerns.
Octane rating is a measure of a fuel’s ability to resist knocking in an internal combustion engine. Knocking is a pre-ignition of the fuel-air mixture in the engine cylinder, which can cause engine damage. TEL increases the octane rating of gasoline by acting as a “lead scavenger.” Lead scavengers react with the free radicals that are formed during combustion, which prevents them from causing pre-ignition.
TEL was first introduced as a gasoline additive in 1921. It quickly became the most widely used octane booster, and it was used in virtually all gasoline until the 1970s. However, TEL is a toxic substance that can cause a variety of health problems, including brain damage, kidney damage, and cancer. In addition, TEL is a major source of lead pollution. Lead is a neurotoxin that can cause developmental problems in children, and it can also cause a variety of health problems in adults.
Due to the environmental and health concerns associated with TEL, it was phased out of use in the United States in the 1970s. However, it is still used in some countries, such as China.
The other options are incorrect because they are not used to increase the anti-knocking property of petrol.