Which of the following hazardous chemical is used as anti-knocking agent in gasoline:

Another prominent lead product was tetraethyl lead, a gasoline additive invented in 1921 to solve "knocking" problems that had become commonplace with the development of high compression engines operating at high temperatures. Soon after reaching its peak 50 years later, the use of this lead compound declined as the installation of catalytic conveers became mandatory on the exhaust systems of passenger cars and also by environment protection laws. Ref :