Modes of occurrence of Metals:- the elements generally occur in the free state or in the combined state. This is mainly because of different chemical reactivities of elements.

i)             Native State: - the elements which have very low reactivity and have little or no affinity for oxygen or air, moisture, carbon dioxide or other non metals occur in the free state, called native state. For example, nitrogen, noble gases, metals like gold, silver, platinum, etc. occur in nature in the native state. Therefore, these elements are also called native elements.

ii)           Combined state:- the elements which are reactive and have a tendency to combine with oxygen or air moisture, carbon dioxide and non metals like carbon, nitrogen, sulphur, phosphorus, arsenic, halogen, etc. occur in the combined state. Therefore, these elements occur in the crust of the earth in the form of their compounds. In the combined state the non metals are usually found in the reduced form and the metals in the oxidized form.