Molecules
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50 free Molecules trivia questions with answers — science & nature quiz, new questions added Oct 2026.
Everything you can touch, taste or smell is made of atoms, and most of the time those atoms travel in groups. A molecule is one of those groups: two or more atoms joined so firmly that they behave as a single unit. Water, sugar, the air in the room and the scent of a cut lemon are all molecules at work. This quiz covers the ground a middle school or early high school science unit does. There are questions on how atoms hold on to each other, the words chemists use to sort molecules into families, and why the shape of a molecule matters. Plenty more are about famous molecules in the kitchen, the body and the sky, along with the scientists who showed that molecules are real long before anyone could see one. The opening questions suit curious beginners and younger students. The later ones reach toward what a chemistry class meets before a test. Every answer comes with a short explanation, so a wrong guess still teaches something new.
30 of 50 questions with answers and explanations. Play the quiz
Q 01Which gas, a molecule of three oxygen atoms, forms a high layer that shields Earth from the Sun's ultraviolet rays?
Ozone
Ozone takes its name from the Greek word for smell, after the sharp odour it leaves in the air following a lightning strike. The oxygen people breathe has only two atoms in each molecule.
Q 02Which gas that humans breathe out freezes into dry ice, the solid that makes stage fog without ever melting?
Carbon dioxide
Carbon dioxide has no liquid stage at normal air pressure, so dry ice turns straight from a solid into a gas at about −78 °C. The name dry ice began life as a 1925 trademark.
Q 03What does water do as it freezes, unlike most liquids, because its molecules lock into an open six-sided pattern?
It expands
It expands by about 9%, which makes ice less dense than liquid water, so ice floats. That is why ponds freeze from the top down instead of from the bottom up.
Q 04Which molecule do coffee and tea plants make as a natural pesticide that can paralyse and kill feeding insects?
Caffeine
Caffeine is the world's most widely consumed psychoactive drug. In flower nectar a small dose seems to sharpen a honey bee's memory of the reward, so the bee keeps coming back.
Q 05Which cleaning product, made in Babylon around 2800 BC, has molecules with a water-loving head and a grease-loving tail?
Soap
Soap molecules wrap specks of grease in tiny spheres called micelles, tails pointing in and heads pointing out. Plain water can then rinse the trapped dirt away.
Q 06Which American founding father calmed a London pond with a teaspoon of oil, a film later shown to be one molecule thick?
Benjamin Franklin
Benjamin Franklin watched the oil smooth the waves across about half an acre of the pond at Clapham Common. Over a century later Lord Rayleigh measured how thin such an oil film is.
Q 07Which gas, one carbon atom bonded to four hydrogens, is the main ingredient of natural gas and is belched out by cows?
Methane
Methane has no smell of its own, so a strong-smelling additive goes into household gas to make leaks noticeable. Cattle belch most of theirs out as gut microbes ferment their food.
Q 08Which gas, whose paired atoms are locked together by a very strong triple bond, makes up about 78% of Earth's air?
Nitrogen
Nitrogen molecules are so hard to split that most living things cannot use the gas straight from the air. Lightning and certain bacteria break the bond and turn it into plant food.
Q 09Which kitchen staple, a crystal lattice of sodium and chloride ions, contains no separate molecules at all?
Table salt
Table salt has six neighbours of the opposite charge around every ion, so no pair belongs together as one molecule. Dissolving it in water pulls the lattice apart ion by ion.
Q 10Which molecule makes chilli peppers burn by tricking the nerve sensors that normally detect scalding heat?
Capsaicin
Capsaicin puts off mammals, whose teeth crush the seeds, but birds cannot feel it at all. Birds swallow the seeds whole and scatter them, which suits the plant nicely.
Q 11Which everyday measurement, bottoming out at absolute zero, tracks how fast a substance's molecules are jiggling?
Temperature
Temperature reflects the average energy of motion of the particles in a substance. Robert Hooke argued for the link in a lecture in 1681, long before anyone could prove that molecules exist.
Q 12Which property of water, caused by its molecules clinging to one another, lets water striders walk across a pond?
Surface tension
Surface tension can hold up things denser than water, such as a steel razor blade laid flat. The same inward pull rounds falling water into droplets.
Q 13Which process, the drift of molecules from crowded places to emptier ones, moves oxygen from the lungs into the blood?
Diffusion
Q 21Which word describes a substance like water, whose molecules contain more than one element, unlike oxygen gas?
Compound
A compound can behave nothing like its ingredients. Water puts out fires, yet it is built from hydrogen, which burns, and oxygen, which feeds flames.
Q 22Which word, built on the Greek for two, describes the molecules of oxygen and hydrogen gas, each a bonded pair?
Diatomic
Diatomic hydrogen is the lightest molecule of all, so light that it escapes Earth's atmosphere faster than heavier gases. Bromine forms the same kind of pairs as a liquid.
Q 23Which word describes giant molecules, such as rubber, nylon and DNA, built from long chains of small repeating units?
Polymer
Diffusion is passive, so the body spends no energy on it. Randomly jostling molecules simply spread from where they are crowded to where they are scarce.
Q 14Which Italian scientist, trained as a lawyer, gives his name to the number of molecules in one mole of a substance?
Amedeo Avogadro
Amedeo Avogadro never knew the number that carries his name. The French physicist Jean Perrin coined the term in 1909, more than fifty years after the Italian's death.
Q 15Which family of elements, including neon and argon, exists as lone atoms because it almost never bonds into molecules?
Noble gases
Noble gases have a full outer shell of electrons, which leaves them little reason to react. Argon was even named after the Greek word for lazy.
Q 16Which simple sugar do plants build in photosynthesis and animals carry in the blood as fuel for their cells?
Glucose
Glucose is the most abundant simple sugar in nature. Plants also chain thousands of its units together to make cellulose, the tough material of their cell walls.
Q 17Which sugar in milk can most of the world's adults no longer digest fully, for lack of an enzyme?
Lactose
Lactose takes its name from the Latin word for milk. Babies make the enzyme that splits it, but in most people the supply fades after childhood, except among peoples with a long history of herding.
Q 18Which painkiller, first sold worldwide by the German firm Bayer, is a lab-made relative of a remedy from willow bark?
Aspirin
Aspirin began as Bayer's own brand name, and the company later lost the trademark in many countries. Willow remedies appear on clay tablets from ancient Sumer.
Q 19Which molecule, water with one extra oxygen atom, bleaches hair and helps bombardier beetles fire a boiling spray?
Hydrogen peroxide
Hydrogen peroxide slowly breaks down in light, which is why pharmacies sell it in brown bottles. All it leaves behind is water and oxygen.
Q 20Which type of chemical bond, the kind holding a water molecule together, forms when atoms share pairs of electrons?
Covalent
Covalent bonds are a partnership: the 'co' in the name means jointly, as in co-operate. The American chemist Irving Langmuir coined the term in 1919.
Polymer comes from the Greek for many parts. Nature got there long before the plastics industry: silk, wool and the cellulose in wood are all long chain molecules.
Q 24Which term, from the Greek for equal parts, describes molecules with the same formula but differently arranged atoms?
Isomers
Isomers can behave very differently despite their identical ingredients. One form of the molecule carvone smells of spearmint, while its mirror-image twin gives caraway seeds their smell.
Q 25Which word describes a molecule such as water, with a slightly positive end and a slightly negative end?
Polar
Polar molecules try to line up with an electric field, and a microwave oven exploits that. Its waves keep the water in food spinning, and the motion turns into heat.
Q 26Which shape does a water molecule have, because two unshared pairs of electrons push its hydrogen atoms to one side?
Bent
Bent at about 104.5 degrees, a water molecule ends up slightly negative on its oxygen side and slightly positive on the other. That lopsided charge makes water molecules cling together.
Q 27Which family of molecules, the main ingredients of petrol and candle wax, contains only two kinds of atom?
Hydrocarbons
Hydrocarbons contain nothing but hydrogen and carbon, yet they range from lighter gas to petrol to solid wax. Crude oil, natural gas and coal are their main natural sources.
Q 28Which poisonous gas with no smell or colour, made when fuel burns without enough air, do household alarms detect?
Carbon monoxide
Carbon monoxide grips the oxygen-carrying protein in blood about 240 times more strongly than oxygen does. Even a little in the air crowds out the oxygen the body needs.
Q 29Which ring-shaped molecule's structure did August Kekulé say came to him in a daydream of a snake biting its tail?
Benzene
Benzene is a flat hexagon of six carbon atoms, each holding one hydrogen. Michael Faraday first isolated it in 1825 from the oily residue left by making gas for lamps.
Q 30Which American chemist won a Nobel Prize for explaining the chemical bond and a second for campaigning for peace?
Linus Pauling
Linus Pauling is the only person to have won two unshared Nobel Prizes. The peace award was announced on the very day a treaty limiting nuclear weapons tests came into force.