Hydrogen is the most abundant element in the universe, making up about 75% of all normal matter by mass. It is the lightest and simplest element with one proton. Helium is second most abundant at about 24%, formed by hydrogen fusion in stars.
Chemistry is the science of matter - the fundamental discipline that investigates what everything in the universe is made of, how different substances interact with one another, and why these interactions produce the dazzling variety of materials, phenomena, and processes that make up the world we inhabit. Chemistry explains why iron rusts in the presence of water and oxygen, why bread rises in an oven, why diamonds are hard enough to scratch glass, why certain plants are poisonous, and why the medicines we take are able to interact specifically with the biological machinery of our bodies. In a very real sense, chemistry is the science that explains everything. The periodic table of elements - one of the greatest intellectual achievements in the history of science - is chemistry's master key. In a single, elegantly organized chart, it encodes the identities and properties of all 118 known types of atoms, from hydrogen - the lightest and most abundant element in the universe - to oganesson, the most recently synthesized superheavy element, which exists only fleetingly in the conditions created inside particle accelerators. The table reveals, through its very structure, the hidden patterns and regularities that govern how atoms behave and interact: elements in the same column share similar chemical properties; elements along the same row share the same number of electron shells. When Dmitri Mendeleev first arranged the elements this way in 1869, he left gaps for elements not yet discovered - and he was right. The missing elements were found exactly where he predicted. This quiz tests your understanding of chemistry's most essential and fascinating concepts. What is the most abundant element not just on Earth, but in the entire observable universe - and why does its dominance so profoundly shape the structure of all matter? What does the pH scale measure, and what does it mean for a substance to be acidic, basic, or neutral? Why is diamond - a substance composed entirely of the same carbon atoms found in graphite and soot - the hardest natural material on Earth? What is the difference between an exothermic and an endothermic chemical reaction, and how do you recognize each from its effects on the surrounding environment? You will also explore the chemistry of everyday life: the explosive fizzing that occurs when baking soda meets vinegar, the structure of the water molecule that gives it so many of its extraordinary properties, and the branch of organic chemistry that underpins everything from pharmaceuticals to plastics. Chemistry is not confined to laboratories - it is happening inside your body and around you at every moment, in every substance you touch, taste, smell, and breathe.