This episode explores the life and legacy of Amedeo Avogadro, the Italian scientist whose work laid the foundation for modern chemistry. In 1811, Avogadro proposed that equal volumes of gases, at the same temperature and pressure, contain the same number of molecules—a principle now known as Avogadro's Law. Although his ideas were initially ignored, they later became central to the development of atomic theory and the ideal gas law. His name is now associated with Avogadro's number (6.022 × 10²³), which links the microscopic world of atoms to measurable quantities in the lab. Despite not receiving recognition during his lifetime, Avogadro's work profoundly transformed how we understand matter, paving the way for precise chemical measurement and molecular science.