Question 12
In the early 20th century, Marie and Pierre Curie were working on radioactivity of pitchblende, known by then to contain the element uranium. However, they found anomalous trace quantities of another material that were much more radioactive than uranium. After labouring for several months, exhausting all physical and chemical processes to extract and purify the material, they were able to make measurements of its physical properties. This was a sign that they discovered a new: