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This science trivia quiz has 100 free questions with answers spanning physics, chemistry, biology, astronomy, earth science and the human body: which gas plants breathe in, what the chemical symbol for gold is, how many bones an adult has, why the sky is blue and what a light-year actually measures. Most questions sit at a middle-school level, so it works as 7th grade science trivia for a classroom warm-up or family quiz, and the harder stretch will stretch high school students and adults who think they remember it all. Every answer has been checked against a reliable reference source, and each question shows a short explanation once you have answered so the quiz teaches as it goes. Play it through for a shareable score, then try the Science Trivia for Kids and Space quizzes for more.
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Q 01What is the chemical symbol for gold?
Au
Au comes from the Latin 'aurum'; gold is so unreactive that it is one of the few metals found in nature as nuggets of pure metal.
Q 02Which planet is the only one less dense than water?
Saturn
Saturn has a mean density of about 0.69 g/cm³, the only planet below water's 1 g/cm³, so it would float in a large enough ocean; Jupiter is roughly twice as dense.
Q 03Which organelle is nicknamed the 'powerhouse of the cell'?
Mitochondria
Mitochondria, which carry their own small circular genome, inherited only from your mother, because they were once free-living bacteria that moved in. Philip Siekevitz coined the nickname in Scientific American.
Q 04What is the speed of light in a vacuum, approximately?
300,000 km/s
The speed of light in a vacuum is approximately 299,792 kilometers per second (about 300,000 km/s). It is the universal speed limit according to Einstein's theory of special relativity.
Q 05Which scientist is credited with developing the theory of general relativity?
Albert Einstein
Albert Einstein published general relativity in 1915, and Arthur Eddington's 1919 eclipse expedition confirmed it by measuring starlight bending around the Sun by the amount he predicted.
Q 06What is the hardest natural substance on Earth?
Diamond
Diamond, which is hard but not tough: hardness is resistance to scratching, and a hammer blow along a cleavage plane will split it. It is pure carbon, the same stuff as pencil graphite, arranged differently.
Q 07What gas makes up approximately 78% of Earth's atmosphere?
Nitrogen
Nitrogen makes up about 78% of dry air, with oxygen near 21%; argon, not carbon dioxide, is the third most plentiful gas at just under 1%.
Q 08What is the largest organ in the human body?
Skin
Skin accounts for roughly 16% of body mass and is constantly renewed, shedding its outer layer every few weeks.
Q 09Which element has the atomic number 1?
Hydrogen
Hydrogen, the lightest and simplest atom, and the fuel the Sun burns by fusing it into helium. Nearly everything heavier was cooked inside stars.
Q 10What phenomenon causes the Northern Lights?
Solar particles exciting gases in the upper atmosphere
Excited oxygen produces the familiar green glow, while nitrogen adds blues and purples; the same process over the South Pole is the aurora australis.
Q 11What is the chemical formula for table salt?
NaCl
NaCl, sodium chloride: sodium explodes in water and chlorine was a First World War weapon, yet bonded together they season dinner. The 'Na' comes from the Latin natrium.
Q 12Which blood type is considered the universal donor?
O negative
Only about 7% of people are O negative, so blood banks prize it for emergencies when there is no time to type a patient.
Q 13What is the most abundant protein in the human body?
Collagen
Collagen makes up roughly a quarter to a third of all the body's protein, forming the fibrous scaffolding of skin, tendon, bone and cartilage; its triple-helix structure gives it tensile strength.
Q 21What is the pH of pure water at room temperature?
7
Pure water at 25 °C has a pH of 7, the neutral point, though it drifts slightly below 7 as water warms; the scale itself was devised by Danish chemist Søren Sørensen in 1909.
Q 22Which planet is known as the Red Planet?
Mars
Mars, which is rusty because its iron-rich dust oxidised long ago, and it also hosts the tallest volcano in the Solar System, Olympus Mons, about two and a half times the height of Everest.
Q 23What is the function of white blood cells?
Fight infections
Fight infections, which is why a high count is a sign the body is at war. Red cells outnumber them about 700 to one, and platelets, not white cells, do the clotting.
Q 14Who discovered penicillin?
Alexander Fleming
Fleming noticed the mould in 1928 after returning from holiday to find it had killed the bacteria on a neglected culture plate.
Q 15What is the unit of electrical resistance?
Ohm
Its symbol is the Greek capital omega, and its inverse, the unit of conductance, was cheekily named the 'mho'.
Q 16What type of rock is formed from cooled lava or magma?
Igneous
Igneous rocks form when molten rock (magma or lava) cools and solidifies. Examples include granite (formed underground) and basalt (formed from surface lava flows).
Q 17What is the closest star to Earth after the Sun?
Proxima Centauri
Proxima Centauri is about 4.24 light-years from Earth. It is a small red dwarf star in the Alpha Centauri star system and has at least two confirmed exoplanets.
Q 18Which vitamin is produced when human skin is exposed to sunlight?
Vitamin D
Ultraviolet B (UVB) radiation from sunlight triggers vitamin D synthesis in the skin. Vitamin D is essential for calcium absorption and bone health.
Q 19What is the process by which plants convert sunlight into energy?
Photosynthesis
Photosynthesis takes place in chloroplasts, where light energy drives the reactions that build sugars; the gas plants release in the process is, chemically, their waste. Every breath you take is a plant's rubbish.
Q 20What is the Heisenberg Uncertainty Principle about?
Position and momentum cannot both be known exactly
Werner Heisenberg showed in 1927 that a particle's position and momentum cannot both be known exactly; the product of their uncertainties has a floor set by Planck's constant, a property of nature rather than of instruments.
Q 24What force keeps planets in orbit around the Sun?
Gravity
Gravity, and an orbit really is a fall: the planet drops toward the Sun but its sideways speed carries it past, over and over. Newton worked this out with a cannonball fired ever faster from a mountaintop.
Q 25What is the most common element in the Earth's crust?
Oxygen
Nearly half the crust's mass is oxygen locked up in silicate and oxide minerals; silicon comes second at roughly 28%.
Q 26Who proposed the heliocentric model of the solar system?
Nicolaus Copernicus
Nicolaus Copernicus published his heliocentric model in 1543, proposing that the Earth and other planets revolve around the Sun rather than everything orbiting Earth.
Q 27What is the smallest unit of matter that retains the properties of an element?
Atom
Atom, from the Greek atomos, 'uncuttable', a name coined long before anyone knew atoms could be split; an atom of gold keeps gold's chemistry, but its separated parts do not.
Q 28What is the name of the supercontinent that existed about 250 million years ago?
Pangaea
Pangaea was the supercontinent that contained all present-day continents. It began breaking apart about 200 million years ago due to plate tectonics, eventually forming the continents we know today.
Q 29What particle in an atom has a negative charge?
Electron
Electron, about 1,800 times lighter than a proton, and its charge, minus 1.6 × 10⁻¹⁹ coulombs, is the basic unit of electricity. Current in a wire is electrons shuffling along.
Q 30What is the normal resting heart rate for adults?
60–100 bpm
A normal adult resting heart rate is 60–100 bpm; elite endurance athletes can rest in the 40s because each beat pumps more blood.