The correct answer is option 'C', benefaction of ore.

The process of separating gangue and other impurities from the metals is known as benefaction of ore. This process is commonly used in the extraction of metals from their ores. The main objective of benefaction is to concentrate the valuable minerals by selectively removing the unwanted gangue and impurities.

There are several methods used for benefaction of ores, including:

1. Crushing and Grinding: The ore is first crushed and ground into smaller particles. This helps in increasing the surface area of the ore and liberating the valuable minerals from the gangue.

2. Gravity Separation: This method utilizes the differences in density between the ore minerals and gangue minerals. It is based on the principle of settling velocity, where the heavier particles settle faster and are separated from the lighter particles. Gravity separation methods include jigging, shaking tables, and spiral concentrators.

3. Magnetic Separation: This method is used to separate magnetic minerals from non-magnetic minerals by utilizing the magnetic properties of the minerals. The ore is subjected to a magnetic field, and the magnetic particles are attracted to the magnetic surface, while the non-magnetic particles remain unaffected. This is commonly used for the separation of iron ores.

4. Froth Flotation: This method is used for the concentration of sulphide ores. It involves the addition of chemical reagents to selectively render the desired minerals hydrophobic, while the gangue remains hydrophilic. The ore is then agitated with air bubbles, and the hydrophobic minerals attach to the air bubbles and rise to the surface as froth, which is then collected and further processed.

5. Leaching: This method is used for the extraction of soluble minerals from ores. It involves the dissolution of the desired minerals in a suitable solvent, followed by the separation of the solution from the insoluble gangue. Leaching is commonly used for the extraction of gold and silver from their ores.

In conclusion, benefaction of ore is the process of separating gangue and other impurities from the metals. It involves various methods such as crushing, grinding, gravity separation, magnetic separation, froth flotation, and leaching, depending on the nature of the ore and the desired minerals.