Sodium is a soft, silvery coloured metal which, like other members of the alkali group of metals, is extremely reactive.         As for the other members of the group, it can be prepared by electrolysis of the fused halide or hydroxide. Sodium is the most common alkali metal and the sixth most abundant element on Earth, comprising 2.8 percent of Earth’s crust.    primarily as the carbonate, chloride or nitrate. Molten sodium is used as a heat exchanger in certain types of nuclear reactors and as a reagent in the chemicals industry. Some of the sodium salts e.g. NaCl and NaCO₃) are more important than the metal itself due to the variety of applications for which they can be used.