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50 free Hydrogen trivia questions with answers — science & nature quiz, new questions added Aug 2026.
This hydrogen trivia quiz covers the lightest and most abundant element in the universe. The easy questions handle the basics: its symbol and atomic number, what its name means, what happens when it burns, and why it once lifted airships until the Hindenburg put a stop to that. The harder end digs into the chemistry and physics: the three isotopes and their names, why heavy water matters to nuclear reactors, tritium's half-life and its use in glowing watch dials, the ortho and para spin isomers, James Dewar liquefying it in 1898, the metallic phase thought to exist inside Jupiter, the 21-centimetre line astronomers use to map the cosmos, the Haber process, steam methane reforming, and how the first neutral atoms formed 370,000 years after the Big Bang. Every answer was checked against the element's encyclopaedia entry before publishing and the supporting sentence is stored with each question. Our periodic table, chemistry and helium quizzes are the natural next stop.
30 of 50 questions with answers and explanations. Play the quiz
Q 01What is hydrogen's atomic number?
1
Its symbol is H, and its most common isotope is nothing more than one proton and one electron.
Q 02Roughly what share of all normal matter in the universe is hydrogen?
About 75%
By number of atoms rather than mass it is even more dominant, above 90%.
Q 03Under standard conditions, hydrogen gas is made of molecules with which formula?
H2
The official name is dihydrogen; the gas is colourless, odourless, non-toxic and highly combustible.
Q 04Who identified hydrogen as a distinct substance between 1766 and 1781?
Henry Cavendish
He suspected the gas was the mythical phlogiston itself and is usually credited with discovering the element.
Q 05What does the name 'hydrogen' mean?
Water-former
It comes from the Greek hudor (water) and gennao (I bring forth), because burning it produces water.
Q 06What did Cavendish originally call the gas he made from a metal-acid reaction?
Inflammable air
Fixed air was carbon dioxide and dephlogisticated air was oxygen, in the vocabulary of the day.
Q 07Which chemist named the element after reproducing, with Laplace, the finding that burning it makes water?
Antoine Lavoisier
He also produced it by passing steam through a red-hot iron tube for his experiments on the conservation of mass.
Q 08Which Irish scientist described in 1671 the hydrogen-releasing reaction of iron filings with acids?
Robert Boyle
He never noted the gas was flammable, but the gas would later help topple the phlogiston theory.
Q 09How many naturally occurring isotopes does hydrogen have?
Three
Uniquely among elements, each of them has its own name; heavier ones up to 7H exist only briefly in labs.
Q 10What is the rarely used formal name for the common isotope 1H, whose nucleus is a single proton?
Protium
It is the only stable isotope of any element with no neutrons at all.
Q 11Deuterium's nucleus contains one proton and how many neutrons?
One
Nearly all the deuterium in the universe was made in the first minutes after the Big Bang and has survived ever since.
Q 12What is the name for H2O in which deuterium replaces ordinary hydrogen?
Heavy water
Nuclear reactors use it as a neutron moderator and coolant; it is not radioactive.
Q 13What is the half-life of tritium?
12.32 years
It beta-decays into helium-3, and is radioactive enough to power luminous paint on watch dials and exit signs.
Who discovered deuterium in December 1931?
Q 21At atmospheric pressure, to roughly what temperature must hydrogen be cooled to be fully liquid?
About 20 K
That is -253 C; the melting point where it turns solid is a touch lower at 14 K.
Q 22Metallic hydrogen, a conductor formed at extreme pressure, is believed to exist deep inside which planet?
Jupiter
It takes pressures beyond 400 billion pascals, about 58 million psi.
Q 23In which form does hydrogen exist inside stars?
Plasma
Ionised hydrogen is a soup of free protons and electrons; the Sun is mostly this.
Q 24Who invented the first hydrogen-filled balloon, in 1783?
Harold Urey
His group found the deuterium-rich form of water the following year; tritium was prepared in 1934 by Rutherford, Oliphant and Harteck.
Q 15Why can't the symbol P be used for hydrogen-1, the way D and T are used for deuterium and tritium?
P was already taken by phosphorus
IUPAC allows D and T but prefers 2H and 3H in its guidelines.
Q 16What is the antimatter counterpart of the hydrogen atom made of?
An antiproton and a positron
Muonium, an antimuon plus an electron, is another exotic hydrogen-like atom that IUPAC even names compounds for.
Q 17Hydrogen flames are hard to see in daylight because they emit mostly what?
Faint blue and ultraviolet light
Special flame detectors are used at plants because a burning leak can be nearly invisible.
Q 18Hydrogen forms explosive mixtures with air across roughly what concentration range?
4% to 74%
With chlorine the range is even wider, 5% to 95%; the autoignition temperature in air is 500 C.
Q 19Molecular hydrogen exists as two spin isomers. What are they called?
Ortho and para
At room temperature the mix is about 75% ortho; converting to para releases enough heat to boil off liquid hydrogen if not handled during cooling.
Q 20Who first liquefied hydrogen, in 1898?
James Dewar
He used regenerative cooling and his own invention, the vacuum flask, and made solid hydrogen the next year.
Jacques Charles
Giffard's 1852 airship was the first reliable powered flight, and Zeppelin's rigid airships followed from 1900.
Q 25Hydrogen has roughly what fraction of the density of air?
About 7%
That buoyancy is why it filled balloons and airships, and why it still lifts weather balloons in place of pricier helium.
Q 26Which hydrogen airship burned over New Jersey on 6 May 1937, ending commercial airship travel?
The Hindenburg
Before World War I, Zeppelins had carried 35,000 passengers without a serious incident.
Q 27Which British airship made the first non-stop transatlantic crossing, in 1919?
R34
Regular passenger airship service resumed in the 1920s and lasted until 1937.
Q 28What is the medium-strength attraction formed when H is bonded to fluorine, oxygen or nitrogen called?
Hydrogen bonding
It shapes boiling points, viscosity, solubility and even how proteins fold.
Q 29In the Bronsted-Lowry theory, acids are defined as donors of what?
Protons
A bare proton cannot survive in solution, so chemists talk about the hydronium ion H3O+ instead.
Q 30What is the negatively charged hydrogen ion, H-, called?
Hydride
Gilbert N. Lewis suggested it existed in 1916; it is rarely seen because it strips protons from solvents to make H2.