Chemists say that caesium is the most active metal in the world. The metal is used in spacecraft propellants and atomic clocks. The highly-reactive metal is also employed for radiation therapy of the cancer patients.
However, caesium is one of the most unpredictable metals as well given that it transforms itself and can wreak everything around it by exploding.
Caesium is one of the softest and the most reactive metals included in the periodic table. When exposed to open air, the metal ignites spontaneously. Even if caesium is dipped in water as cold as -116 degree Celsius ( -177 degree Fahrenheit), it will explode.
On top of it all, caesium does not occur abundantly in nature and thus, is even more expensive than gold. Caesium also transforms its shape and produces beautiful, metallic snowflakes as its temperature is varied.
You can see various experiments with Cesium tried by the YouTuber Thoisoi in the video below: