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Calcium is a chemical element with symbol Ca and atomic number 20. Calcium is a soft grayish-yellow alkaline earth metal, fifth-most-abundant element by mass in the Earth's crust. The ion Ca2+ is also the fifth-most-abundant dissolved ion in seawater by both molarity and mass, after sodium, chloride, magnesium, and sulfate. Free calcium metal is too reactive to occur in nature. Calcium is produced in supernova nucleosynthesis. Calcium has a wide variety of applications, almost all of which are associated with calcium compounds and salts. CalciumCalcium metal is used as a deoxidizer, desulfurizer, and decarbonizer for production of some ferrous and nonferrous alloys. In steelmaking and production of iron, Ca reacts with oxygen and sulfur-containing impurities.
Molybdenum is a chemical element with symbol Mo and atomic number 42. The name is from Neo-Latin molybdaenum, from Ancient Greek Μ?λυβδοςmolybdos, meaning lead, since its ores were confused with lead ores.