The long-standing model of pigment cell origins is implicitly based upon a progressive fate restriction model of neural crest development and postulates the existence of a partially restricted progenitor common to all pigment cell types (i.e., a chromatoblast) [38] .
Sodium is the fourth most abundant element on earth, comprising about 2.6% of the earth's crust; it is the most abundant of the alkali group of metals. It is now obtained commercially by the electrolysis of absolutely dry fused sodium chloride.
A: Sodium belongs to the family of elements called alkali metals. The atomic number of sodium is 11 and its atomic weight is 22.98976928 atomic mass units or grams per mole. The symbol for sodium is Na. The electronic configuration of sodium is [Ne] 3S1 and it has one valence electron in the outermost shell.