Beyond the answers - interesting background to this quiz

A capital on the Mekong

Phnom Penh has been Cambodia's capital since the country regained independence, and it sits where the Mekong, Tonle Sap and Bassac rivers meet. The city's name is usually linked to a legendary woman, Penh, said to have found Buddha statues in a floating tree and built a shrine on the spot. Today it is both the political centre and the largest city in Cambodia.

Riga and the Baltic stage

Riga, the Latvian capital, grew wealthy in the Middle Ages as a member of the Hanseatic League, a trading network that linked ports across northern Europe. Its old town is famous for one of Europe's finest collections of Art Nouveau buildings. Latvia itself regained independence in 1991 and later joined both the European Union and NATO.

Cicero, Rome's word merchant

Cicero was a Roman statesman, lawyer and writer whose speeches and letters survive in remarkable quantity. He held the office of consul in 63 BC, the highest elected position in the Roman Republic, and his writing shaped Latin prose for centuries. His letters also give historians a rare, personal view of Roman politics in crisis.

Nitrogen: the quiet majority

Earth's atmosphere is roughly 78 per cent nitrogen, with oxygen making up about 21 per cent. Nitrogen is chemically fairly unreactive, which is why it does not simply burn away or react with everything around it. Life depends on it anyway: nitrogen is essential to proteins and DNA, and crops rely on fertilisers that fix it into usable forms.

Mercury, the metal world

Mercury is the smallest planet in the solar system and the closest to the Sun. It is also unusually dense, with a huge iron core that makes up much of its volume, which is why it is often described as the most metallic of the planets. With almost no atmosphere to trap heat, surface temperatures swing between extremes.