Which of the following elements was NOT discovered by Marie Curie?

Marie Curie is renowned for her pioneering research on radioactivity and her discovery of the elements radium and polonium. Her work involved isolating these two elements from uranium ore. She conducted groundbreaking experiments that enhanced our understanding of atomic physics and radioactivity.

Uranium itself was discovered prior to Curie's research by several scientists in the early 19th century, so it is not attributed to her discoveries. Furthermore, thorium, which was first identified by Jons Jakob Berzelius in 1828, also predates Curie's work and is thus not part of her contributions to science.

By recognizing that radium and polonium were isolated through Curie’s investigative efforts while uranium and thorium were earlier identified by others, it clarifies that thorium did not originate from her discoveries. Therefore, recognizing which elements form part of Marie Curie's significant contributions to science helps highlight the historical context of her work in the field of nuclear physics.