Which element did Marie Curie discover first?

Marie Curie discovered polonium first, before radium.

In July 1898, Marie and Pierre Curie announced the existence of polonium while studying pitchblende, a uranium ore. The mineral was unexpectedly more radioactive than its known uranium content could explain, leading them to suspect that it contained previously unknown radioactive substances.

They named the new element polonium after Marie’s homeland, Poland, which was then partitioned among Russia, Prussia, and Austria-Hungary and did not exist as an independent state. The name was both a scientific label and a public reminder of Poland’s political situation.

The Curies announced a second new element, radium, in December 1898. This timing creates the most common quiz confusion: both elements are central to their work, but polonium came first. Their investigations also helped establish the concept and terminology of radioactivity. Polonium was initially identified through its intense radiation rather than through a large, pure sample, and isolating these substances required processing enormous quantities of ore.