Chlorine
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40 free Chlorine trivia questions with answers — science & nature quiz, new questions added Oct 2026.
Chlorine is one of the few elements most people have smelled, or think they have. It keeps swimming pools and tap water safe, it is locked inside every grain of table salt, and in its pure form it is a poison that changed the history of warfare. This quiz turns the best chlorine fun facts into multiple-choice questions: who discovered the gas and how it got its name, what it does inside the human body, how it cleaned up drinking water, and the plastics, medicines and household products built on it. Every answer comes with a short explanation. It suits chemistry students revising the periodic table, teachers looking for a lively lesson starter, and anyone who enjoys a surprising science fact.
30 of 40 questions with answers and explanations. Play the quiz
Q 01The so-called chlorine smell at swimming pools actually comes from which compound, formed when chlorine meets sweat?
Chloramine
Chloramine forms when free chlorine reacts with compounds in sweat and other body waste, so the famous pool smell is not the element itself.
Q 02Soldiers gassed with chlorine in World War I said it smelled like pepper mixed with which tropical fruit?
Pineapple
Pineapple and pepper was how survivors described the smell, and they also reported a metallic taste that stung the back of the throat.
Q 03Before proper gas masks, World War I troops facing chlorine were told to breathe through cloths soaked in what?
Urine
Urine was advised because its urea was thought to react with chlorine and blunt it, and the order went down the line within days of the first attack.
Q 04Which Hungarian doctor slashed deaths in a Vienna maternity ward by making staff wash their hands in chlorine solution?
Ignaz Semmelweis
Ignaz Semmelweis chose chlorine because it removed the smell of the dissecting room from doctors' hands, which soap alone did not.
Q 05Which artificial sweetener, sold under the Splenda brand, is table sugar with three chlorine atoms swapped in?
Sucralose
Sucralose is about 600 times sweeter than sugar, and it was reportedly found when a researcher misheard an order to test a chlorinated compound as taste.
Q 06Vinyl records are pressed from which chlorine-rich plastic, also used for water pipes and window frames?
PVC
PVC is the world's third most produced plastic, and chlorine makes up more than half of its weight.
Q 07What in the human body makes its own hypochlorous acid, the germ-killer in chlorinated pools, to destroy bacteria?
White blood cells
White blood cells called neutrophils turn chloride ions into hypochlorous acid, a bleach-like weapon they use against invading microbes.
Q 08The human stomach uses chlorine taken from salt in food to make which corrosive chemical for digestion?
Hydrochloric acid
Hydrochloric acid brings the stomach's contents down to a pH between 1 and 3, strong enough to act as a barrier against swallowed microbes.
Q 09Which sweet-smelling chlorine compound did Queen Victoria inhale for pain relief during two of her childbirths?
Chloroform
Chloroform was given to the queen by physician John Snow, the same doctor linked to the famous cholera outbreak around London's Broad Street pump.
Q 10Chlorine atoms released by CFC gases from old fridges and spray cans destroy which protective part of the atmosphere?
Ozone layer
Ozone layer damage is so efficient because each chlorine atom works as a catalyst, breaking up ozone molecules over and over without being used up.
Q 11The name chlorine comes from the Greek word khloros, which describes the gas as which colour?
Pale green
Pale green is the meaning of the Greek khloros, the same root that gives the leaf pigment chlorophyll its name.
Q 12Table salt is chlorine bonded to which soft, silvery metal that reacts fiercely with water?
Sodium
Sodium is a highly reactive metal and chlorine is a poison gas, yet joined together they make a seasoning the body cannot live without.
Q 13Chlorine gas made its battlefield debut in April 1915 near which Belgian town on the Western Front?
Ypres
Ypres was where German troops opened 5,730 cylinders and let the breeze carry the gas across to the Allied lines.
Q 21America's first continuously chlorinated water supply served which community on the Hudson River, facing Manhattan?
Jersey City
Jersey City began treating its Boonton Reservoir supply in 1908, and within a decade the US Treasury was calling for all drinking water to be chlorinated.
Q 22Which World War I poison gas, made from chlorine and carbon monoxide, smells faintly of freshly mown hay?
Phosgene
Phosgene was harder to detect than chlorine and far more lethal, and it is blamed for about 85,000 deaths in the war.
Q 23Which German chemist, later a Nobel laureate, personally oversaw the first chlorine gas attack of World War I?
Fritz Haber
Fritz Haber argued that gas was no crueller than bullets, and he is remembered as the father of chemical warfare.
Q 14Chlorine, fluorine and iodine belong to which family of elements, whose name is Greek for salt producer?
Halogens
Halogens was a label first coined for chlorine alone in 1811, and only later stretched to cover its whole column of the periodic table.
Q 15Which British chemist, inventor of the miners' safety lamp, proved in 1810 that chlorine was an element?
Humphry Davy
Humphry Davy repeated an experiment that two French chemists had given up on, decided the gas could not be broken down, and gave it the name it still has.
Q 16Which Swedish chemist is credited with discovering chlorine in 1774 but took it for a compound, not a new element?
Carl Wilhelm Scheele
Carl Wilhelm Scheele made the gas from a manganese mineral and noted that it bleached litmus and killed insects.
Q 17Which chlorine-based insecticide was banned in the United States after Rachel Carson attacked it in Silent Spring?
DDT
DDT was so prized at first that the Swiss scientist who found its insect-killing power won a Nobel Prize, years before its harm to wildlife came to light.
Q 18NASA's Phoenix lander found perchlorate, a chlorine-rich salt toxic to people, in the soil of which world?
Mars
Mars has perchlorate spread through its soil, where the salt works like antifreeze and could let briny water stay liquid for a few hours on summer days.
Q 19Mixing chlorine bleach with which other common household cleaner produces toxic, lung-burning fumes?
Ammonia
Ammonia reacts with bleach to form poisonous gases, and one of the products, nitrogen trichloride, is explosive as well.
Q 20Which chlorine-containing herbicide did American aircraft spray over jungle to strip away cover during the Vietnam War?
Agent Orange
Agent Orange blended two chlorinated weedkillers and carried traces of a chlorine-based dioxin, a contaminant linked to cancer.
Q 24Which British scientist, best known for his work on electricity and magnetism, first turned chlorine into a liquid?
Michael Faraday
Michael Faraday liquefied chlorine in 1823, and he also discovered tetrachloroethylene, the chlorine-rich liquid that later became a leading dry-cleaning solvent.
Q 25Which French chemist first used chlorine gas on cloth and created the bleach known as Javel water?
Claude Berthollet
Claude Berthollet made the liquid in 1789 at his laboratory on the Javel quay in Paris, which is how the bleach got its name.
Q 26Which chlorine-bearing acid mixture, known to alchemists for centuries, is famous for dissolving gold?
Aqua regia
Aqua regia hid two gold Nobel Prize medals from the Nazis in World War II, when a chemist in Copenhagen dissolved them and left the jar on a shelf.
Q 27Which inherited disease is diagnosed with a sweat test measuring chloride, the ion form of chlorine?
Cystic fibrosis
Cystic fibrosis damages the channels that move chloride in and out of cells, so far more of it than normal ends up in a patient's sweat.
Q 28Which element, a red-brown liquid at room temperature, is used like chlorine to disinfect swimming pools?
Bromine
Bromine kills germs much as chlorine does but keeps working across a wider pH range, which makes it a good choice for indoor pools.
Q 29Which chlorine-containing synthetic rubber, invented at DuPont in 1930, is the usual material for wetsuits?
Neoprene
Neoprene is built from chloroprene, a chlorine-bearing molecule, and the foamed form traps heat well enough to insulate divers and surfers.
Q 30Chlorine has caused swimming pool ceilings to collapse by cracking rods made of which normally rust-proof metal?
Stainless steel
Stainless steel is not alone in cracking under chlorine attack: the same kind of damage ruined plastic plumbing joints across the US in the 1980s and 1990s.