Beyond the answers - interesting background to this quiz

A capital that shares its country's name

Luxembourg is one of the few countries in the world whose capital city carries the same name as the nation itself. The city grew up around a medieval fortress perched on steep cliffs, and its old quarters and fortifications are recognised as a UNESCO World Heritage Site. Today it is a financial centre and one of the three official seats of the European Union's institutions, alongside Brussels and Strasbourg.

Why Mercury's surface tells an old story

Mercury is the smallest planet in the solar system and the closest to the Sun, and its surface is covered in craters that have barely changed in billions of years. Unlike Earth, it has no real atmosphere to erode features or weather them away, and little geological activity to reshape the crust. That is why scientists often describe it as a fossil of the early solar system, a place where impacts from long ago are still written on the ground.

One letter, several elements

The chemical symbol C belongs to carbon, but the letter also appears inside the symbols of other elements, such as Co for cobalt and Ca for calcium. Carbon is unusual for its ability to bond with itself in long chains and rings, which is the basis of organic chemistry and of all known life. Pure carbon turns up in strikingly different forms, from soft graphite in pencils to diamond, one of the hardest natural materials.

Egypt's many names

Ancient Egyptians called their land Kemet, usually translated as "the black land", a reference to the dark, fertile soil left behind by the Nile's annual floods. They contrasted it with "the red land", the surrounding desert. Over the centuries the country has been known by many other names in different languages, and the name Egypt itself comes to us through Greek. Siam and Batavia, by the way, were old names for Thailand and Jakarta respectively.

A river that stays within one country

The Yangtze is the longest river in Asia and the third longest in the world, and it flows entirely within China. It rises on the Tibetan Plateau and travels roughly 6,300 kilometres before reaching the sea near Shanghai. Along the way it passes through the famous Three Gorges, a region now also associated with one of the largest hydroelectric dams ever built.