Strontium
Strontium is a chemical element with a Sr symbol and an atomic number 38. Sr are chemically reactive or soft white silvery silvery elements. This alkaline metal turns yellow when exposed to air. It occurs naturally in selestin and strontianit minerals. The 90Sr isotope exists in radioactive fall and has half life at 29.10 years. Its name comes from the Strontia word a village in Scotland, as it has been found nearby.