Question

The antiknock agent added to unleaded petrol is-
a. Tetraethyl lead
b. Tetramethyl lead
c. Dibromoethane
d. Methyl Tertiary Butyl Ether (MTBE)

Answer 1

Hint: The anti-knocking agents are the compounds added to the petrol engine in limited quantities to reduce the propensity to knocking. This compound is intended to reduce emissions of carbon monoxide and ozone in the environment.

Complete answer:
> Option A is incorrect. Tetraethyllead (TEL) is a compound of organ lead with formula $(CH_{3}CH_{2})_{4}Pb$. It is a petro-fuel additive, first mixed with gasoline starting in the 1920s as a patented octane rating booster that allowed a significant increase in engine compression. This in turn caused the vehicle efficiency and fuel economy to improve. In the 19th century, General Motors research laboratory, which had spent several years trying to find an additive that was both highly effective and inexpensive, discovered its antiknock potency in 1921.

> Option B is incorrect. Tetramethyl lead is a chemical compound used as a gasoline antiknock additive. For environmental considerations the use is phased out. Tetramethyl lead exposure can affect the central nervous system, the kidney and the cardiovascular system. Tetramethyl lead can be ingested through inhalation, contact with the eyes, absorption of the skin and ingestion of the material. Exposure signs include insomnia, coma, paralysis, mania, delirium, appetite loss, nausea, hypotension, anxiety, restlessness, and nightmares.

> Option C is incorrect. 1,2-Dibromoethane (EDB) is an organ bromine compound, also known as ethylene dibromide. While trace amounts occur naturally in the ocean, where they are likely produced by algae and kelp, they are mostly synthetic. It is a thick colourless liquid with a sweet odour that can be detected at 10 ppm and is a commonly used and sometimes provocative fumigant. The combustion of 1,2-dibromoethane produces highly corrosive, hydrogen bromide gas. It's been used in soil and on various crops as a pesticide. It happens to be used as a fumigant to treat termites and beetles’ leaves, to monitor the moths in beehives.

> Option D is correct. MTBE is an additive to fuel, used as an oxygen to increase the number of octanes. It is one of a group of chemicals widely known as oxygenates, since they increase gasoline's oxygen content. It was used in low-level gasoline to replace tetraethyl lead, and to improve its octane value to help avoid knocking of the engine. Oxygenates tend to more thoroughly consume oil, producing $CO_2$ emissions instead of $CO$.

Hence, The correct answer is option (D).

Note: Lead is not being used as it has had significant harmful environmental consequences and emits unfriendly gases such as $CO$ and nitrogen oxides. Methyl tertiary butyl ether is also added and is easily miscible with petrol. But it has also shown the carcinogenic properties.