Francium
- Francium is a highly radioactive metal and is the heaviest known member of the alkali metal series in the periodic table. It is extremely rare and is primarily of scientific interest due to its instability and rapid decay. nounFrancium is so rare that it is estimated that there is less than an ounce of it on Earth at any given time.Due to its high radioactivity, francium is not used in any practical applications and is mainly studied for research purposes.