A constituent of the exhaust fumes from electricity generating sets which causes serious pollution is

Analyze the question: The question asks which constituent of exhaust fumes from electricity generating sets (petrol or diesel "generators") causes serious pollution.

Concept: Generators burn fuel (petrol or diesel). When combustion is incomplete, because of limited oxygen supply, the exhaust contains:

• Carbon (II) oxide (CO): a poisonous gas
• Carbon (IV) oxide (CO₂), water vapour, and oxides of nitrogen and sulphur, plus soot

Why carbon (II) oxide?

• CO is colourless and odourless, so people don't notice it.
• It combines with haemoglobin in red blood cells to form carboxyhaemoglobin. This is far more stable than oxyhaemoglobin, so blood can no longer carry oxygen properly.
• The result is headache, dizziness, unconsciousness and even death. This is why people die in closed rooms or garages when a generator is running. In Nigeria, such "generator fume" deaths are reported often.

Checking the other options:

• B. Water vapour: harmless, a normal product of combustion.
• C. Ozone: not a direct constituent of exhaust. It forms later in the atmosphere from reactions involving nitrogen oxides and sunlight.
• D. Carbon (IV) oxide: it is a greenhouse gas and is present in the exhaust, but it is not directly poisonous in the way CO is. It is not the best answer for "serious pollution" from the fumes.

Answer: The correct option is A. Carbon (II) oxide.

Exam tip: Remember "incomplete combustion = CO = poisonous." If a question mentions fumes from generators, car exhausts or charcoal fires, think carbon (II) oxide and its effect on haemoglobin.