Why can a faulty gas heater be dangerous even when its flame looks normal?

• It may release CO that you could detect by smell.
• It may release CO only when the flame turns yellow.
• It may release colourless, odourless carbon monoxide.

Which pair is produced by complete combustion of a hydrocarbon in enough oxygen?

• Carbon monoxide and water
• Carbon dioxide and water
• Carbon dioxide and hydrogen

Sulfur dioxide released by burning sulfur-containing fuel can contribute to acid rain.

A supplier wants less sulfur dioxide to form when its fuel burns. Which change addresses that pollutant's source?

• Reduce the fuel's sulfur content
• Increase the air supply
• Fit a catalytic converter to the exhaust

Nitrogen is normally unreactive. Why can engines still make nitrogen oxides from air?

• Nitrogen oxides enter ready-made with the air.
• High temperatures let nitrogen and oxygen react.
• The catalyst in the exhaust makes them from nitrogen.

A power plant fits scrubbers to remove sulfur dioxide from flue gas. Which evaluation gives a benefit and a cost?

• They cut SO2 and use no energy.
• They cut CO but use energy and materials.
• They cut SO2 but use energy and materials.

A town has no nearby fuel-burning plants. A student says this rules out acid rain caused by fuel emissions. Why does that conclusion not follow?

• Winds can carry the source gases from distant places.
• Acid rain forms only when gases stay beside their source.
• Rain carries acids only after source gases settle on local soil.

Someone has headaches in a room with a fuel-burning heater and notices soot nearby. Carbon monoxide is suspected. What is the safest next action?

• Open a window, then wait beside the heater.
• Leave for fresh air, tell an adult and get emergency help.
• Switch the heater off, then stay to check the flame.