IMO Practice Test — Combustion and Flame
6 Questions • 15 min • Olympiad level
15:00
Question 1 of 6
Sand is thrown on a small fire to put it out because the sand:
Cuts off the air (oxygen) supply
Adds fuel
Raises the temperature
Adds oxygen
Explanation: Sand covers the fire and cuts off oxygen, removing one side of the fire triangle.
Question 2 of 6
A matchstick lights at once but a coal piece needs much heating. This is because they have different:
Ignition temperatures
Colours
Weights only
Smells
Explanation: Coal has a much higher ignition temperature than the matchstick head.
Question 3 of 6
Why is a stove flame adjusted to burn blue rather than yellow for cooking?
A blue flame means complete combustion and more heat with less soot
A blue flame is colder
A yellow flame is hotter
A blue flame uses no fuel
Explanation: A blue flame shows complete combustion, giving more heat and less smoke/soot.
Question 4 of 6
CO2 is a good fire extinguisher for electrical fires mainly because it:
Does not conduct electricity and cuts off oxygen
Adds oxygen
Is a fuel
Conducts electricity well
Explanation: CO2 is non-conducting and smothers the fire by cutting off oxygen, safe for electrical fires.
Question 5 of 6
Of two fuels, one leaves a lot of ash and smoke while the other burns cleanly with a high calorific value. The better fuel is the one that:
Burns cleanly with high calorific value
Leaves more ash
Produces more smoke
Gives less heat
Explanation: A good fuel gives a lot of heat and burns cleanly with little ash and smoke.
Question 6 of 6
Burning fossil fuels releases carbon dioxide, which contributes to:
Global warming
Cooling the Earth
Cleaner air
Making fuels renewable
Explanation: Carbon dioxide is a greenhouse gas that contributes to global warming.