Beyond the answers - interesting background to this quiz

The tiny republic that shares its capital's name

San Marino, landlocked inside central Italy, is one of the world's smallest and oldest republics, and it is unusual in that the city of San Marino is itself the capital. The country's founding is traditionally dated to 301 AD, when, according to tradition, a stonemason named Marinus established a small community on Mount Titano. Over the centuries it kept a distinct identity despite being surrounded by larger Italian states, and it remains an independent republic today.

Why the Dead Sea is so salty

The Dead Sea sits in a deep basin at the lowest land elevation on Earth's surface, and water can only leave it by evaporation. Because dissolved minerals stay behind when water evaporates, salt and other compounds have concentrated there over a very long time, making it far saltier than ordinary seawater. That density is why swimmers float so easily - and why fish cannot survive in it, hence the name.

Agatha Christie and the train that made her famous

Murder on the Orient Express, published in 1934, is one of Agatha Christie's best-known novels and features her Belgian detective Hercule Poirot. Christie drew on the real Orient Express, the long-distance passenger train that linked Western Europe with Constantinople, and on a famous real-life incident in which a train was stranded by heavy snow. The book's confined setting and closed circle of suspects became a template for much detective fiction that followed.

Nickel and the trap of similar symbols

Nickel's chemical symbol is Ni, which is easy to confuse with symbols for neighbouring elements. N stands for nitrogen, while Ne is neon - so the quiz's three options are all real symbols, just for different elements. Nickel itself is a hard, silvery metal widely used in alloys such as stainless steel, and it takes its name from a German word meaning something like "false copper", reflecting miners' frustration at ore that looked promising but yielded the wrong metal.

Steinbeck, Oklahoma and the road west

John Steinbeck published The Grapes of Wrath in 1939, and it won the Pulitzer Prize for Fiction the following year. The novel follows the Joad family as they leave drought-stricken Oklahoma during the Great Depression and travel to California in search of work. Steinbeck's unflinching portrayal of poverty and migration made the book both celebrated and controversial, and it remains a central text in American literature.