**19. Nickel**

Nickel is the 7th most abundant transition metal in the earth's crust. The electronic configuration of nickel is [Ar]4S23d8. Nickel occurs in nature as oxide, silicate and sulphide. The typical examples are garnierite and pentlandite. Nickel exhibits +1 to +4 oxidation states. Among them divalent state is most stable. Nickel compounds are generally blue and green in color and are often hydrated. Further, most nickel halides are yellow in color. The primary use of nickel is in the preparation of stainless steel. Nickel is also used in the coloring of glass to which it gives a green hue.
