People who suck petrol with their mouths run the risk of increasing in their blood the concentration of

Analyze the question: Petrol is a fuel, and the question asks which substance in it can build up in the blood of someone who sucks it (siphons it) by mouth and accidentally swallows or inhales some.

Concept: Petrol (gasoline) has long been blended with lead compounds, especially tetraethyl lead, as an anti-knock agent. This leaded petrol was common in Nigeria for many years. Lead is a heavy metal. It is absorbed into the body and accumulates in the blood, bones and organs, causing lead poisoning (plumbism). Its effects include damage to the brain, kidneys and nervous system, anaemia, and learning difficulties.

Step-by-step solution:

1. Petrol is the substance being ingested or inhaled.
2. Check which option is a known toxic additive or contaminant of petrol. • Iron: not a petrol additive, and it is an essential nutrient. • Lead: found in leaded petrol, and toxic. • Calcium: not associated with petrol, and it is needed for bones and teeth. • Magnesium: not associated with petrol, and it is also an essential mineral.
3. Lead is the only one that is both linked to petrol and a poison that accumulates in blood.

Answer: B. lead

Tip: For questions on "heavy metal poisoning," remember these pairs:

• Lead → petrol, paints, batteries
• Mercury → contaminated fish, thermometers
• Cadmium → batteries

Also note that siphoning petrol by mouth is dangerous for other reasons too. It can cause chemical pneumonia if petrol gets into the lungs.