Quiz of the Day
Chemistry & the Periodic Table
Friday, 23 October 2026
Anchored to Mole Day (Oct 23), explore the elements, chemical reactions, famous chemists, and the everyday chemistry all around us
1. Mole Day is celebrated on October 23 in honour of Avogadro's number. What is that number, approximately?
- 6.022 × 10²³
- 9.81 × 10²³
- 3.14 × 10²³
- 1.602 × 10¹⁹
Avogadro's number, about 6.022 × 10²³, is the count of particles in one mole of a substance. Mole Day is celebrated each year from 6:02 a.m. to 6:02 p.m. on October 23, a playful nod to '6.02' and '10/23'. It is named after Amedeo Avogadro, though he never actually calculated the value himself.
2. What is the chemical symbol for gold?
- Au
- Gd
- Go
- Ag
Gold's symbol Au comes from its Latin name 'aurum', meaning 'shining dawn'. Many element symbols derive from Latin rather than English, such as Fe for iron ('ferrum') and Pb for lead ('plumbum'). Ag, a common wrong guess, is actually the symbol for silver, from the Latin 'argentum'.
3. Which element has atomic number 1, making it the lightest and most abundant element in the universe?
- Hydrogen
- Helium
- Carbon
- Oxygen
Hydrogen sits first on the periodic table with a single proton. It makes up roughly 75% of the normal matter in the universe by mass and fuels the fusion reactions inside stars, including our Sun. On Earth it is most familiar bound up in water.
4. What is the chemical formula for water?
- H₂O
- O₂
- H₂O₂
- CO₂
Water is two hydrogen atoms bonded to one oxygen atom, giving the formula H₂O. Its bent molecular shape makes it polar, which is why water is such a good solvent for so many substances. The similar-looking H₂O₂ is hydrogen peroxide, a very different and reactive compound.
5. Which element is the most abundant gas in Earth's atmosphere?
- Hydrogen
- Oxygen
- Carbon dioxide
- Nitrogen
Nitrogen gas makes up about 78% of the air we breathe, well ahead of oxygen at around 21%. The nitrogen molecule (N₂) is held together by a strong triple bond, which makes it fairly unreactive. That stability is why so much energy is needed to 'fix' nitrogen into fertilisers.
6. Which gas do green plants absorb from the air to carry out photosynthesis?
- Nitrogen
- Carbon dioxide
- Oxygen
- Hydrogen
Plants take in carbon dioxide and, using sunlight and water, produce sugars while releasing oxygen. This process, photosynthesis, is the ultimate source of nearly all the oxygen in our atmosphere. In effect, plants breathe in what animals breathe out, and vice versa.
7. What does the pH scale measure?
- Temperature
- How acidic or alkaline a solution is
- Density
- Pressure
The pH scale runs from 0 to 14, with 7 being neutral, lower values acidic, and higher values alkaline (basic). It is a logarithmic scale, so each whole step represents a tenfold change in acidity. Lemon juice sits around pH 2, while household bleach is close to pH 13.
8. Who is credited with publishing the first widely recognised periodic table of the elements in 1869?
- Dmitri Mendeleev
- Antoine Lavoisier
- John Dalton
- Marie Curie
Russian chemist Dmitri Mendeleev arranged the known elements by atomic weight and recurring properties. His table famously left gaps for elements not yet discovered, and he even predicted their properties, which were later confirmed. This power to forecast new elements is what set his version apart from earlier attempts.
9. Which metal is represented by the chemical symbol Fe?
- Fluorine
- Iron
- Francium
- Fermium
Iron's symbol Fe comes from the Latin 'ferrum'. It is one of the most abundant elements on Earth and forms most of the planet's core. Iron is also essential to life, sitting at the heart of the haemoglobin molecule that carries oxygen in our blood.
10. Which metal is a liquid at ordinary room temperature?
- Caesium
- Bromine
- Mercury
- Gallium
Mercury is the only metal that is liquid at standard room temperature, which earned it the nickname 'quicksilver'. Bromine is also liquid at room temperature, but it is a non-metal, not a metal. Gallium and caesium are solids that melt just slightly above room temperature, so gallium can famously melt in your hand.
11. Marie Curie won Nobel Prizes in which two different scientific fields?
- Chemistry and Medicine
- Chemistry and Peace
- Physics and Chemistry
- Physics and Medicine
Marie Curie won the Nobel Prize in Physics in 1903 and in Chemistry in 1911, making her the first person to win Nobel Prizes in two different sciences. She remains the only person ever to do so. Her research on radioactivity, a term she coined, transformed both physics and chemistry.
12. Which is the lightest of the noble gases?
- Neon
- Argon
- Radon
- Helium
Helium is the lightest noble gas and the second lightest element overall, after hydrogen. Because it is far less flammable than hydrogen, it is used to fill airships and party balloons. Helium was actually detected in the Sun's spectrum before it was ever found on Earth, which is why it is named after 'Helios', the Greek Sun god.
13. Marie and Pierre Curie discovered two elements in 1898. Which one did they name after Marie's native country?
- Radium
- Uranium
- Thorium
- Polonium
Polonium was named after Poland, the homeland of Marie Curie, who was born Maria Sklodowska in Warsaw. She chose the name partly to draw attention to Poland, which at the time was not an independent nation. The Curies discovered both polonium and radium while studying the mineral pitchblende.
14. Which 18th-century French scientist is often called the 'father of modern chemistry' for helping establish the law of conservation of mass?
- John Dalton
- Robert Boyle
- Joseph Priestley
- Antoine Lavoisier
Antoine Lavoisier showed through careful measurement that mass is conserved in chemical reactions and helped name oxygen and hydrogen. He also helped develop a systematic method for naming chemical compounds still reflected today. Tragically, he was executed by guillotine during the French Revolution in 1794.
15. Which element has the highest melting point of any metal, at around 3,422°C?
- Osmium
- Tungsten
- Titanium
- Rhenium
Tungsten melts at about 3,422°C, the highest melting point of any metal. This extreme heat resistance is why it was long used for the glowing filaments in incandescent light bulbs. Its name comes from Swedish for 'heavy stone', and its symbol W comes from the older name 'wolfram'.