In this chemistry lesson, students learn about the chemical properties of hydrogen, focusing on its reactions with oxygen, chlorine, and copper dioxide. The lesson revisits how hydrogen is produced when metals like sodium and potassium react with water, forming a basic solution and releasing hydrogen gas in an exothermic reaction. The instructor explains the differences in reactivity among metals, noting that less reactive metals such as gold and silver do not react with water or acids, making them valuable for jewelry.