Beyond the answers - interesting background to this quiz

The number that defines an element

The number of protons in a nucleus is what chemists call the atomic number, and it is the single most important fact about an element. Change the proton count and you no longer have the same element: hydrogen has one, helium two, carbon six. Neutrons can vary within an element, creating isotopes, but the proton tally stays fixed. That is why the periodic table is arranged by atomic number rather than by mass.

A border shaped by geography and history

Ecuador sits on the Pacific coast of South America and shares land borders with just two countries: Colombia to the north and Peru to the east and south. Its name comes from the equator, which runs through the country. The border with Peru was only settled after a long-running territorial dispute that flared into war in 1941 and was finally resolved by a treaty signed in 1998.

Why table tennis balls barely weigh anything

A table tennis ball is hollow, made of plastic and weighs only about 2.7 grams, which makes it dramatically lighter than a football, a rugby ball or a tennis ball. That lightness is central to the sport: it allows players to impart heavy spin and send the ball flying at speeds that can exceed 100 km/h. The ball's official diameter of 40 mm has been fixed since 2000, when it was increased slightly from 38 mm to slow the game down for television.

Brussels, a capital with more than one identity

Brussels is the capital of Belgium, but it also functions as the de facto capital of the European Union, hosting the European Commission, the Council of the European Union and part of the European Parliament. The city is officially bilingual, with French and Dutch as its two main languages, and it sits in a country that is itself divided into Dutch-speaking Flanders, French-speaking Wallonia and the bilingual Brussels-Capital Region.

The tango's journey from the docks to the world

Tango emerged in the late nineteenth century in the working-class neighbourhoods of Buenos Aires, Argentina, shaped by a mix of European immigrant and local influences. It spread to Europe in the early twentieth century and became a global phenomenon, with Paris particularly embracing it. In 2009, UNESCO added Argentine and Uruguayan tango to its list of intangible cultural heritage, recognising both the dance and its accompanying music.