Beyond the answers - interesting background to this quiz

A document signed in the shadow of war

The United Nations came into being in 1945, when delegates from fifty countries met in San Francisco and signed the UN Charter. The organisation replaced the League of Nations, which had failed to prevent the Second World War. Its founding principle was collective security: an attack on one member would be treated as an attack on all.

An instrument that travelled the world

Scotland is the country most closely associated with the bagpipes, but the instrument is far older and more widespread than many people assume. Early forms appear in ancient Egypt, Rome and Persia, and versions are still played across Spain, Turkey, India and the Balkans. What makes Scottish piping distinctive is the great Highland bagpipe, with its three drones and piercing chanter, adopted by Highland regiments and later by pipe bands worldwide.

The century that shaped Frida Kahlo

Frida Kahlo was most active as an artist in the twentieth century, and her life was as dramatic as her canvases. A bus accident in 1925 left her with injuries that troubled her for the rest of her life, and she began painting while recovering in bed. Her work blends Mexican folk culture, personal suffering and bold self-portraiture, and she became a central figure in Mexico's artistic renaissance alongside her husband, Diego Rivera.

Maxwell, the quiet giant of physics

James Clerk Maxwell formulated the laws of electromagnetism in the nineteenth century, unifying electricity, magnetism and light into a single theory. His equations predicted that light itself is an electromagnetic wave, a claim later confirmed by Heinrich Hertz. Albert Einstein kept a portrait of Maxwell on his study wall, and his work directly paved the way for relativity and modern physics.

The year the polio vaccine arrived

Jonas Salk's polio vaccine was developed in 1955, the same year it was declared safe and effective. Polio had paralysed hundreds of thousands of children worldwide, and the news triggered scenes of public celebration. Salk famously refused to patent the vaccine, asking whether it was possible to patent the sun. His rival Albert Sabin later developed an oral version that became the standard in many countries.