Francium is a highly radioactive alkali metal with the symbol Fr and atomic number 87. It is one of the rarest elements in the Earth's crust, primarily found in trace amounts in uranium and thorium ores. Due to its extreme radioactivity, francium is highly unstable and has a very short half-life, making it difficult to study. Discovered in 1949 by Marguerite Perey, francium is the least stable of the first 101 elements on the periodic table. It is known for its intense radioactivity and is primarily of interest in scientific research rather than practical applications. Its properties are similar to those of other alkali metals like Sodium and Potassium.