Final answer:
After the theory about rays moving through solid objects, Marie Curie decided to investigate the phenomenon of radioactivity, leading to the discovery of polonium and radium and advancement in the understanding of the chemical composition and radioactivity of elements.
Step-by-step explanation:
According to the sequence chart, the event that happened directly after the development of the theory that rays can travel through solid objects was Marie Curie deciding to investigate the claim. Marie Curie, together with her husband Pierre Curie, conducted extensive research into radiation phenomena, leading to groundbreaking discoveries. After Henri Becquerel's observation that uranium salts emitted rays that could expose photographic plates even when wrapped in black cloth, Marie Curie hypothesized that the chemical composition of uranium might be responsible for this effect. She and Pierre studied the properties of uranium and subsequently discovered two new elements, polonium and radium, which were highly radioactive and contributed to the development of atomic theory. The chemical composition and radioactivity research conducted by the Curies laid the foundation for modern nuclear physics and chemistry.