Oxygen Trivia
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49 free Oxygen trivia questions with answers — science & nature quiz, new questions added Sep 2026.
This oxygen trivia quiz covers the element we breathe and the most abundant one in Earth's crust. The easy questions handle the basics: its symbol and atomic number, how much of the air it makes up, what ozone is, where atmospheric oxygen comes from and who gets credit for discovering it. The harder end digs into the science and the history: why Lavoisier's name for it was based on a mistake, the alchemist who isolated it before 1604, why liquid oxygen is sky blue and sticks to a magnet, the Great Oxygenation Event 2.45 billion years ago, oxygen-18 and ancient climates, how much steelmaking consumes, why the Apollo 1 fire spread so fast, oxygen toxicity for divers, and how airliner masks make their own supply. Every answer was checked against the element's encyclopaedia entry before publishing and the supporting sentence is stored with each question. Our hydrogen, carbon, periodic table and chemistry quizzes are the natural next stop.
30 of 49 questions with answers and explanations. Play the quiz
Q 01What does oxygen's atomic number, 8, actually count?
Protons in its nucleus
Protons in its nucleus: eight of them make an atom oxygen, whatever else it carries. Add or remove a single one and it becomes a different element entirely.
Q 02Roughly what fraction of Earth's atmosphere is oxygen gas, by volume?
About 21%
About 21% goes in with every breath, and most of it comes straight back out: exhaled air still holds around 16% oxygen, which is why mouth-to-mouth rescue breaths can keep someone alive.
Q 03Oxygen is best known as a gas, but where is it the most abundant element of all?
Earth's crust
Earth's crust is nearly half oxygen by weight, locked up with silicon in rock and sand. The air and oceans together hold only a tiny share of the planet's oxygen.
Q 04Oxygen is the universe's third most abundant element; which is second?
Helium
Helium and hydrogen were made in the Big Bang itself. Oxygen came later, forged inside stars by fusing helium and scattered when those stars died.
Q 05What is the chemical formula of ozone?
O3
O3 is ozone: three oxygen atoms in one molecule. Its name comes from the Greek for 'to smell', after the sharp odour it gives the air near electrical sparks and lightning.
Q 06High in the atmosphere, what splits oxygen molecules into the lone atoms that build the ozone layer?
Ultraviolet light
Ultraviolet light from the Sun makes the very shield that blocks it: the atoms it frees build ozone, and that ozone then absorbs more ultraviolet before it can reach the ground.
Q 07Why is Joseph Priestley usually credited with discovering oxygen, though Carl Scheele made it first?
His work was published first
His work was published first. Scheele's book on the gas sat with its printer for two years and came out only in 1777, well after Priestley's account was in print.
Q 08What did Joseph Priestley, a believer in phlogiston theory, name the oxygen he made in 1774?
Dephlogisticated air
Dephlogisticated air was his name because he thought the gas was ordinary air stripped of phlogiston, the supposed essence of fire, and so able to soak up more from a flame and keep it burning longer.
Q 09Who, with Peter Habeler, made the first ascent of Mount Everest without bottled oxygen in 1978?
Reinhold Messner
Reinhold Messner and Habeler did what many doctors and climbers had thought impossible. Two years later Messner went back and climbed Everest without oxygen again, this time entirely alone.
Q 10Octopus and horseshoe crab blood carries oxygen with hemocyanin, which turns blue because it contains which metal?
Copper
Copper turns blue when it binds oxygen. Horseshoe crabs are caught and bled for that blue blood, which is used to test vaccines and injections for bacterial toxins.
Q 11Who first recognised oxygen as an element and correctly explained its role in combustion, in 1777?
Antoine Lavoisier
Antoine Lavoisier heated tin in a sealed vessel and found the metal gained just the weight the trapped air lost. Burning, he argued, takes something from the air rather than giving off 'phlogiston'.
Q 12Oxygen's name means 'acid-former', yet which common acid contains none?
Hydrochloric acid
Hydrochloric acid is only hydrogen and chlorine, as Humphry Davy proved, which sank the idea that oxygen is what makes an acid. By then the name was too well established to change.
Q 13NASA's MOXIE experiment, carried by the Perseverance rover, made oxygen from which gas in the air of Mars?
Carbon dioxide
Q 21Mars owes its red colour to dust rich in which compound of oxygen?
Iron oxide
Iron oxide is the stuff of rust: iron minerals in the Martian soil have combined with oxygen, coating the whole planet in red-brown dust.
Q 22Which part of a cell uses the oxygen you breathe to release energy from food?
Mitochondria
Mitochondria, the cell's 'powerhouses', carry their own DNA, because they descend from free-living bacteria that took up residence inside our distant ancestors' cells.
Q 23Scientists read ancient temperatures from the ratio of oxygen-18 to oxygen-16 preserved in what?
Seashells and ice cores
Carbon dioxide makes up about 95% of Mars's thin air, and MOXIE pulled one oxygen atom off each molecule. Over two years it made 122 grams, about what a small dog breathes in ten hours.
Q 14Which gas do the French still call 'azote', from the Greek for 'lifeless'?
Nitrogen
Nitrogen makes up most of every breath, yet on its own it puts out flames and suffocates animals. English later switched to 'nitrogen', but French and several other languages kept the older name.
Q 15Which chemist assumed water was HO, and so put oxygen's atomic weight at half its true value?
John Dalton
John Dalton could not count atoms, so he assumed the simplest recipe: when two elements form only one known compound, it has one atom of each. For water that guess was wrong.
Q 16To keep liquid oxygen and other liquefied gases cold, James Dewar invented which everyday item in 1892?
The vacuum flask
The vacuum flask began as lab glassware for storing ultra-cold liquids. In 1904 two German glassblowers saw it could keep drinks hot or cold, and sold it as the Thermos.
Q 17Who flew the first liquid-fuelled rocket in 1926, burning gasoline with liquid oxygen?
Robert H. Goddard
Robert H. Goddard's rocket climbed just 12.5 metres and was back on the ground of his Aunt Effie's farm in 2.5 seconds. NASA still ranks that hop alongside the Wright brothers' first flight.
Q 18Oxygen gas is colourless, but what colour is liquid oxygen?
Pale blue
Pale blue, because liquid oxygen absorbs red light. That is a different effect from the blue of the sky, which comes from air molecules scattering sunlight.
Q 19Liquid oxygen clings to a strong magnet because each oxygen molecule has two unpaired what?
Electrons
Electrons normally pair off and cancel each other's magnetism. Oxygen's two loners do not, so the liquid is pulled toward a magnet strongly enough to hang between its poles.
Q 20Which Apollo mission had to abandon its Moon landing after an oxygen tank exploded on the way there?
Apollo 13
Apollo 13 lost the oxygen it needed for both breathing and electrical power, so the three astronauts moved into the lunar module and used it as a lifeboat to loop around the Moon and get home.
Seashells and ice cores both preserve the water of their day. Water with light oxygen-16 evaporates more readily and ends up locked in ice sheets, so in cold spells the sea and its shells grow richer in oxygen-18.
Q 24Which crashed spacecraft returned solar-wind samples showing the Sun has more oxygen-16 than Earth?
Genesis
Genesis hit the Utah desert at about 300 km/h when its parachutes failed to open, shattering its collectors. Scientists still recovered enough solar wind from the wreckage to make the measurement.
Q 25What process produces the free oxygen in Earth's atmosphere?
Photosynthesis
Photosynthesis frees its oxygen from water, not from carbon dioxide: plants and algae use sunlight to pull H2O apart, keep the hydrogen and release the oxygen as waste.
Q 26Which microbes first filled Earth's air with oxygen in the Great Oxidation Event, over two billion years ago?
Cyanobacteria
Cyanobacteria gave off the gas as waste, and it was poison to much of the life of the day. The upheaval may have caused one of Earth's first mass die-offs.
Q 27Which protein in red blood cells binds oxygen and turns bright red as it does?
Hemoglobin
Hemoglobin has a dangerous weakness: it grips carbon monoxide more than 200 times as tightly as oxygen, which is how fumes from a faulty boiler can starve the body of oxygen.
Q 28In which tiny air sacs of the lungs does oxygen pass into the blood?
Alveoli
Alveoli number in the hundreds of millions, and their thin walls add up to some 70 to 80 square metres. Oxygen dissolves poorly, so the lungs need all of that area to absorb enough of it.
Q 29Hospitals rely on oxygen, but which industry is the biggest single user of the commercially produced gas?
Steelmaking
Steelmaking blows pure oxygen into molten iron to burn out carbon and other impurities. That turns a batch into steel in under an hour, where older furnaces needed ten hours or more.
Q 30Ethylene glycol, made in bulk by reacting ethylene with oxygen, is the main ingredient of which car fluid?
Antifreeze
Antifreeze is mostly ethylene glycol, and the same chemical is a raw material for polyester. Oxygen's handiwork ends up in car radiators and polyester clothes alike.