Beyond the answers - interesting background to this quiz

The river that passes through more capitals than any other

The Danube is often called Europe's most international river. It rises in Germany's Black Forest and flows east for roughly 2,850 kilometres before emptying into the Black Sea, passing through or along the borders of ten countries. Four national capitals sit on its banks: Vienna, Bratislava, Budapest and Belgrade. Serbia, the answer here, lies roughly midway along its course, and the river's broad passage through the country is one of its most striking stretches.

A desert belt that runs the width of Africa

The Sahel is a semi-arid band of grassland and savanna that stretches across Africa just south of the Sahara, from the Atlantic coast to the Red Sea. Sudan sits within this belt, which is why it appears among the options. The region is defined less by borders than by climate: rainfall is low and highly seasonal, and the line between desert and savanna shifts from year to year. That variability makes life there a constant balancing act between herders, farmers and the land itself.

Mountains that sit at the heart of Central Asia

The Tien Shan, whose name means "Heavenly Mountains" in Chinese, is a vast range running roughly 2,500 kilometres across Central Asia. Uzbekistan's capital, Tashkent, sits close to the western foothills of the range, and the country shares the wider mountain system with its neighbours. The peaks feed the rivers and irrigation canals that make farming possible in a region otherwise dominated by desert and dry steppe.

Freud's vocabulary and the language of chemistry

Sigmund Freud's name is inseparable from psychoanalysis, and words he popularised - libido, the unconscious, dream interpretation - have long since escaped the clinic and entered everyday speech. Chemistry, meanwhile, has its own naming quirks: iridium takes its symbol Ir from the Latin "iridium", and its name derives from the Latin for "rainbow" because its salts form compounds in many colours.

Roman numerals and the value of order

Roman numerals are additive and subtractive: read left to right, you add values, except when a smaller numeral precedes a larger one, as in IV or IX. So MDXXX is 1,000 + 500 + 10 + 10 + 10, which comes to 1,530 - comfortably larger than CLII (152) or MCL (1,150). It is a reminder that place matters in number systems, just as it does in the rivers and ranges above.