The most hazardous metal pollutant of automobile exhausts is:

Explanation

Lead (Pb) is released by the combustion of petrol because tetraethyl lead is used as an antiknocking agent in petrol. This lead is very harmful and causes plumbism or lead poisoning, which disturbs the nervous system, liver, kidneys in adults and also causes brain damage in children. About 150 to 400 mg of lead is stored in the body of an average adult and blood levels average about 25 mg/100 ml. An increase to 70 mg/100 ml of blood is generally associated with clinical symptoms. Hence a level of 30 mg/100 ml should be considered alarming.