ANS:C - roasting

Heating of an ore below its melting point in the presence of excess air is called "roasting." Roasting is a process used in metallurgy to convert an ore into its oxide form or to remove volatile impurities from the ore. It involves heating the ore in the presence of excess air (oxygen) but below its melting point. The heat causes chemical reactions to occur, resulting in the oxidation of the ore or the removal of volatile components. Roasting is commonly used to prepare sulfide ores for further processing by converting the sulfides into oxides, which can then be subjected to other metallurgical processes such as smelting or leaching. It is an important step in the extraction of metals from their ores. The other options provided have different meanings:

• Calcination: Heating a substance to high temperatures in the absence of air or with limited air to bring about thermal decomposition, such as in the conversion of limestone (calcium carbonate) into lime (calcium oxide).
• Smelting: A process in which a metal is extracted from its ore by heating the ore with a reducing agent (such as coke) in a furnace. Smelting involves melting the ore to separate the metal from its impurities.
• Sublimation: The transition of a substance directly from the solid phase to the gas phase without passing through the intermediate liquid phase, such as in the case of dry ice (solid carbon dioxide) subliming at room temperature and pressure.