On the basis of reactivity, we can classify metals into the following categories:
1. Extraction of High reactivity metals: The metals which are placed at the top of the reactivity series are very reactive. They are never found in nature as free elements, e.g., sodium, potassium, calcium and aluminium. These metals are obtained by electrolytic reduction.
2. Extraction of Moderately reactive metals: The metals in the middle of reactivity series such as iron, zinc, lead, copper are moderately reactive. These elements are present as sulphides or carbonates in nature. Generally metals are obtained from their oxide as compared to their sulphides and carbonates.
3. Extraction of Less reactive metals: The metals which are placed at the bottom of the reactivity series are least reactive. They occur in free state, e.g. gold, silver and copper. Copper and silver are also found in the combined state as sulphide and oxide ores. These metals are obtained from their ores by just heating the ores in air.
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| Position of object | Position of image | Size of image | Nature of image | |
| (a) | ----------------- | At focus $F_2$ | Point image | Real and inverted |
| (b) | At $2 F_1$ | At $2 F_2$ | ---------------- | Real and inverted |
| (c) | Between $F_1$ and O (within focal length) | On the same side (object side) | Very large | --------------- |
