Concept:Petrol may contain lead-based additives that can enter the bloodstream if petrol is sucked by mouth.
Explanation:Tetraethyl lead,
Pb(C2H5)4, was commonly added to petrol to improve engine performance.
When someone sucks petrol with the mouth, they can ingest or inhale this lead compound.
Absorbed lead enters the blood, so the concentration of lead in the blood increases.
This can cause lead poisoning, which is dangerous to health.
The other metals listed,
Fe,
Ca, and
Mg, are not added to petrol for this purpose.
Therefore, the risk is specifically an increased blood lead level.
Answer:Lead, which corresponds to option B.