Beyond the answers - interesting background to this quiz

The gas that made dentists giggle

Nitrous oxide earned its nickname "laughing gas" in the late 18th century, when the English chemist Joseph Priestley first isolated it and experimenters noticed that inhaling it triggered fits of laughter and giddy behaviour. In the 1840s it found a serious purpose: the American dentist Horace Wells famously used it during a tooth extraction, helping to launch modern surgical anaesthesia.

A Parisian novelist who wrote and rewrote

Honoré de Balzac wrote Father Goriot in the 1830s, and it became a cornerstone of his vast series of interconnected novels known as La Comédie Humaine. Balzac was notorious for endless revisions, often reworking proofs so heavily that printers complained. The novel's themes of ambition and sacrifice also inspired later writers, including the young Charles Dickens admirer Émile Zola.

The quiet workhorse of digestion

The liver produces bile, a greenish-yellow fluid that helps break down fats in the small intestine. It is also the body's largest internal organ and performs hundreds of other jobs, from storing energy to filtering toxins. The gall bladder stores the bile between meals, which is why people can live without it after surgery.

Two capitals that are not the obvious choice

Ottawa became Canada's capital in 1857, partly because Queen Victoria wanted a compromise between English-speaking Toronto and French-speaking Montreal. Montevideo, meanwhile, sits on the Río de la Plata in Uruguay, one of South America's smallest countries, and is often confused with Buenos Aires across the water. Both cities reward a closer look.