Radioactivity Discoverer: Henry Becquerel

The discovery of radioactivity is credited to French physicist Henry Becquerel in the year 1896. He observed that uranium salts emitted rays that could penetrate opaque materials and expose photographic plates, even in the absence of external light source. These spontaneous emissions were termed 'radioactivity'.

Scientific Contributions of Other Options

It's useful to understand the contributions of the other scientists mentioned in the options to appreciate the context:

• Otto Hahn: A German chemist and physicist, Otto Hahn is famous for his work on radioactivity, particularly the discovery of nuclear fission in 1938, for which he received the Nobel Prize in Chemistry in 1944. His work significantly advanced the understanding of nuclear reactions but came after Becquerel's initial discovery.
• J.J. Thomson: Sir Joseph John Thomson was an English physicist who is credited with the discovery of the electron in 1897. While his work was crucial in understanding atomic structure and contributed to the field of subatomic physics, he did not discover radioactivity itself.
• John Corbett: Colonel John Ross Corbett was associated with the discovery of quinine, an anti-malarial drug, derived from the Cinchona tree bark. This contribution is in the field of medicine and pharmacology, not radioactivity.

Summary of Discovery

Henry Becquerel's accidental discovery using uranium salts paved the way for further research into radioactivity by scientists like Marie Curie and Ernest Rutherford, leading to significant advancements in physics and our understanding of the atom.