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Every topic page has its own quiz and the full list with the answers marked, ready to read out or print. For five new questions a day, there is daily trivia.
Planets, stars, the Moon and the missions
On which planets does it rain diamonds?
20 questions Play and read → HistoryEmpires, odd true stories and the people in them
Which is older, Oxford or the Aztecs?
20 questions Play and read → Human BodyBones, brain, heart and senses
Are you more human or more bacteria?
20 questions Play and read → OceanThe deep, its creatures and its records
How many hearts does an octopus have?
20 questions Play and read → PsychologyMemory, habits and the biases in your head
Who decides first: you, or your brain?
20 questions Play and read → FoodDishes, origins and the science of taste
Which food can last thousands of years?
20 questions Play and read → AnimalsRecord-breakers and strange habits
What is the biggest cat in the world, and why won't you ever meet one in the wild?
20 questions Play and read → GeographyCountries, flags and natural wonders
Which country in the world has a population under 1,000?
20 questions Play and read → SciencePhysics, chemistry and biology
Why is the sky blue instead of violet or red?
20 questions Play and read → SportsThe Olympics, records and famous rules
Who exactly was banned from the ancient Olympic Games, according to ancient custom?
20 questions Play and read → Music and ArtComposers, pop records and painters
What happened when the crowd erupted after Beethoven's Ninth Symphony premiered?
20 questions Play and read → InventionsWho invented what, and how
What everyday fastener went ten years without its own name?
20 questions Play and read →The mixed questions from the quiz, right answer highlighted and the fact under it.
On which planets does it rain diamonds?
It rains diamonds on Neptune and Uranus. Deep inside the ice giants, crushing pressure squeezes carbon out of methane and compresses it into diamonds that sink toward the core.
Source: NASA
Which is older, Oxford or the Aztecs?
Oxford University is older than the Aztec Empire. Teaching at Oxford began by 1096. The Aztec capital of Tenochtitlán wasn't founded until 1325, more than two centuries later.
Source: University of Oxford
Are you more human or more bacteria?
You carry more bacterial cells than human cells. Current estimates put the ratio at roughly 1.3 bacterial cells for every human cell, most of them living in your gut.
Source: NIH
How many hearts does an octopus have?
Octopuses have three hearts and blue blood. Two hearts pump blood to the gills, one to the body, and copper-based blood makes it blue.
Source: NOAA
Who decides first: you, or your brain?
Your brain can decide seconds before 'you' do. Brain scans can predict simple choices several seconds before people report consciously making them.
Source: Nature Neuroscience (2008)
Which food can last thousands of years?
Honey can stay good for thousands of years. Its low moisture and high acidity keep bacteria from growing, so sealed honey resists spoiling. Pots found in ancient Egyptian tombs are often cited as still preserved.
Source: Smithsonian
What is the biggest cat in the world, and why won't you ever meet one in the wild?
The liger, a lion-tiger cross, is the largest cat of all. A liger is the offspring of a male lion and a female tiger, and it grows bigger than either parent. Males can reach 3 to 3.6 metres long and weigh over 400 kg. They exist only in captivity, because lions and tigers never share a home range in nature.
Source: Wikipedia
Which country in the world has a population under 1,000?
Vatican City has fewer than 900 residents. Vatican City is both the smallest country by area (about 0.44 square kilometers) and by population, with roughly 880 residents. It's an independent state entirely enclosed within the city of Rome.
Source: Britannica
Why is the sky blue instead of violet or red?
Air molecules scatter blue light the most. Sunlight contains every color, but as it passes through the atmosphere, air molecules scatter short, blue wavelengths far more than red or yellow ones, a phenomenon called Rayleigh scattering. Our eyes are also more sensitive to blue than to violet, which scatters even more, so the sky reads as blue rather than violet.
Source: NASA
Who exactly was banned from the ancient Olympic Games, according to ancient custom?
Married women faced a cliff-tossing ban at the ancient Olympics. According to the ancient writer Pausanias, a married woman caught attending the Games could be thrown from a nearby cliff. Unmarried women, however, were allowed to watch, so the ban applied only to wives.
Source: Britannica
What happened when the crowd erupted after Beethoven's Ninth Symphony premiered?
Beethoven never heard his own standing ovation. By 1824 Beethoven was completely deaf, so when the audience at the premiere of his Ninth Symphony burst into thunderous applause, he kept facing the orchestra, unaware. A singer had to gently turn him around so he could finally see the ovation he could never hear.
Source: Britannica
What everyday fastener went ten years without its own name?
The zipper wasn't even called a zipper for its first decade. Gideon Sundback patented his practical slide fastener in 1913, but it was called a "hookless fastener." B.F. Goodrich only coined the name "zipper" in 1923 for the sound it made closing rubber boots, and the catchy name stuck to everything with teeth and a slider.
Source: National Inventors Hall of Fame
Where does a day outlast the entire year?
A day on Venus lasts longer than its year. Venus takes 243 Earth days to spin once on its axis, but only 225 to orbit the Sun, so its day is longer than its year.
Source: NASA
Was Cleopatra closer to the pyramids or the Moon landing?
Cleopatra lived closer to the Moon landing than to the pyramids. The Great Pyramid was finished around 2560 BC. Cleopatra died in 30 BC, about 2,500 years later, but only 2,000 years before Apollo 11.
Source: Britannica
Who has more bones, you or a newborn?
Babies are born with ~300 bones; adults have 206. Many of a baby's bones are separate pieces of cartilage that fuse together as they grow.
Source: Britannica
How much of the ocean have we actually seen?
More than 80% of the ocean has never been explored. We have better maps of the surface of Mars than of our own seafloor.
Source: NOAA
Why do you forget why you entered the room?
Walking through a doorway really does make you forget. Psychologists call it the doorway effect: crossing a boundary cues the brain to archive one scene and load the next.
Source: Quarterly Journal of Experimental Psychology
Which is the real berry, banana or strawberry?
Bananas are berries but strawberries aren't. Botanically, a berry grows from one flower with one ovary: bananas qualify, strawberries don't.
Source: Britannica
Which mountain big cat can growl and mew but never manages a roar?
The snow leopard is a big cat that cannot roar. Unlike lions and tigers, snow leopards lack the throat structure needed to roar, so they hiss, growl and mew instead. Their thick, metre-long tail helps them balance on cliffs and doubles as a scarf they wrap around their face against the Central Asian cold.
Source: WWF
Which country's flag had no stripes, no stars, no emblem, just one plain color?
Libya's flag was once a single block of green. From 1977 to 2011, Libya flew a solid green flag with no design of any kind, the only national flag of its era to feature just one color and no markings. It was replaced after the 2011 revolution.
Source: Wikipedia
240: 20 in each of the 12 topics, every one with three answers and the fact behind the right one, plus five a day on the daily trivia page. Lock&Learn holds about 1,480 facts across the same topics.
Yes. Read them out, print the page (the right answers are marked) or play the quiz on a shared screen. Each question has one right answer and two plausible wrong ones, and the fact under it gives you something to say after the reveal. Please do not republish the questions elsewhere.
Every fact names its source under the answer, from space agencies and museums to encyclopedias and published research. Lock&Learn writes each one as a teaser question with three answers, and the fact that settles it.
Install Lock&Learn, then touch and hold your Lock Screen, tap Customize, tap the widget area and choose Lock&Learn. A question waits on every screen-wake; you guess, tap, and reveal the verified fact behind the answer. Pick the topics you like and the widget rotates through them.
Yes. Lock&Learn is free on iOS: every topic opens with a free preview and another question unlocks daily. Lock&Learn+ is an optional upgrade that opens every topic in full.