Beyond the answers - interesting background to this quiz

The simplest element and its confusing neighbours

Hydrogen's symbol is H, which looks almost too easy next to its periodic table neighbours. Mercury hides behind Hg, from the Latin hydrargyrum, meaning "liquid silver", while helium takes He. Hydrogen sits at number one because it has a single proton, and it is by far the most abundant element in the universe, even though it makes up only a tiny fraction of Earth's atmosphere.

Where the mud really bubbles

Azerbaijan is the world's mud volcano capital, with hundreds of them concentrated around the Absheron Peninsula and the Caspian Sea coast. These aren't fiery mountains like their magma-driven cousins: they erupt cold mud, gas and water, sometimes building cones tall enough to be mistaken for small hills. Locals have long treated the mud as a health remedy, and some eruptions have been dramatic enough to make international news.

One river, many passports

The Danube is the most international river in the world, flowing through ten countries: Germany, Austria, Slovakia, Hungary, Croatia, Serbia, Romania, Bulgaria, Moldova and Ukraine. It rises in Germany's Black Forest and empties into the Black Sea, passing through four capital cities along the way - Vienna, Bratislava, Budapest and Belgrade. That reach has made it a trade route and a cultural thread linking Central and Eastern Europe for centuries.

Goulash: Hungary's signature in a bowl

Goulash, or gulyas, began as a herdsman's dish cooked outdoors in a heavy pot over an open fire. Its defining ingredient is paprika, the ground red pepper that Hungary embraced after it arrived from the Americas via the Ottoman world. What many visitors call goulash is actually a thick soup, while the stew-like version served with dumplings is closer to what Hungarians call porkolt.

Estonia's money and the euro switch

Estonia adopted the euro in 2011, becoming the first former Soviet republic to join the eurozone. Before that, the country used the kroon, a currency tied to the German mark and later the euro itself. The lek belongs to Albania, and the ruble to Russia, which makes Estonia's euro membership a neat symbol of its westward economic shift.