The element known for being highly reactive and commonly used in fireworks is potassium. Potassium belongs to the alkali metal group of the periodic table and is characterized by its high reactivity, especially with water and air. Due to this reactivity, it must be stored under oil or in an inert atmosphere. In fireworks, potassium compounds, such as potassium nitrate, are often used as oxidizers and contribute to vibrant colors and effects. The presence of potassium can create bright whites and purples in fireworks displays. Its use highlights the fascinating chemistry behind pyrotechnics.