Beyond the answers - interesting background to this quiz

A capital that comes in two parts

Sri Lanka is one of the few countries with two official capital cities, and the quiz answer names both. Colombo remains the commercial heart and the country's largest city, while Sri Jayawardenepura Kotte, a suburb to the south-east, serves as the administrative and legislative capital. The arrangement dates from the 1980s, when the seat of government was moved out of Colombo. It is a useful reminder that "capital city" does not always mean a single, obvious place.

The quiet logic of Roman numerals

CM looks cryptic, but the system has a simple rule: a smaller numeral placed before a larger one is subtracted. So C (100) before M (1000) gives 900. The same trick produces IV for 4 and IX for 9. Roman numerals still turn up on clock faces, film credits, monarchs' names and the occasional Super Bowl, which is why they remain worth recognising even in an age of Arabic digits.

Prime numbers and the trouble with big ones

A prime number is divisible only by 1 and itself, which is why 17 qualifies while 87 (3 x 29) and 27 (3 x 9) do not. Primes are the building blocks of arithmetic: every whole number greater than 1 can be broken down into them. They also underpin modern encryption, since multiplying two large primes is easy but factoring the result back apart is extremely hard. That difficulty keeps bank cards and private messages safe.

Why some elements hide behind odd symbols

Zinc's symbol, Zn, is easy to guess, but thulium's Tm is less obvious - it comes from Thule, an old name for a far northern region. Several element symbols are rooted in Latin or place names rather than modern English: iron is Fe from ferrum, gold is Au from aurum, and tungsten is W from wolfram. The periodic table is therefore a small museum of language history as well as a map of chemistry.