Pu, or plutonium, is a radioactive chemical element with the symbol Pu and atomic number 94. It is a silvery-gray metal that is dense and heavy, often used in nuclear reactors and atomic bombs. Discovered in 1940, plutonium is produced from uranium in nuclear reactors and can be used as fuel for generating electricity. Due to its radioactivity, plutonium must be handled with care. It has a long half-life, meaning it remains hazardous for thousands of years. Scientists study plutonium to understand its properties and potential uses, as well as to manage its environmental impact and safety concerns.