Radioactive elements are substances that emit radiation as they decay. This process occurs when the nucleus of an unstable atom breaks down, releasing energy in the form of particles or electromagnetic waves. Common examples of radioactive elements include uranium, thorium, and radium. These elements are found naturally in the Earth's crust and can also be produced artificially in laboratories. The radiation emitted by radioactive elements can be harmful to living organisms, but it also has practical applications. For instance, radioactive isotopes are used in medical imaging and cancer treatment. Additionally, nuclear power plants harness the energy from radioactive decay to generate electricity, showcasing both the risks and benefits of these elements.