1. A highly radioactive metallic chemical element with atomic number 87, belonging to the alkali metal group.
Usage: chemistry; symbol: Fr; extremely rare and unstable in nature

Examples

• Francium is one of the rarest elements found in Earth's crust.
• The discovery of francium completed the alkali metal group on the periodic table.
• Francium atoms decay rapidly, making it difficult to study in laboratories.
• Scientists use particle accelerators to create francium isotopes for research.
• Francium has the lowest electronegativity of all elements.