Which methods are usually employed for purifying the following metals:
a) Nickel
b) Germanium?
Mention the principle behind each one of them.

Hint: Elements are arranged in a tabular form called periodic table and there are 115 elements present in the periodic table. There are similarities as well as differences in the properties of these elements. On the basis of these properties elements can be divided into metals and non-metals.

Complete answer:
These metals are present in impure form so it is very necessary to purify them by some processes.
 a) Nickel in purified with the help of Mond's process: This process based on the principle that carbon monoxide readily combines with nickel and reversibly able to give nickel carbonyl which is of volatile nature and due to this it readily degrades back into nickel and carbon monoxide at higher temperatures.
b) Germanium is purified with the help of zone refining method. The principle of this method is that impurities are more soluble in molten states of the metal as compared to its solid state. In this process a circular mobile heater is fixed at one end of the rod of an impure metal. With the movement of the heater molten zone also moves and as a result pure metal of the melt crystallizes out and impurities pass on to the adjacent molten zone. This process is repeated many times which leads to segregation of impurities at one end of the rod.

Note:
Metals are arranged on the left side of the periodic table and there are five kinds of metals: Alkaline earth metals, Alkali metals, Transition metals, Actinides and Lanthanides. There are a total 92 elements out of which 70 are metals.