The main function of roasting is
A.to remove the volatile matter
B.to convert the ore into oxide
C.Both (A) and (B)
D.and make slag

Hint: The process of roasting, where ore is heated below its melting point in presence of excess air. Mostly roasting is a process of heating ore for the extraction of metal. It is a metallurgical process where a solid-gas reaction occurs at elevated temperatures to purify the metallic component.

Complete step by step solution:In the metallurgical process of roasting, the ore is heated with a regular supply of air in the furnace at a temperature below its melting point. By this method, the ore is converted into its oxide by continuous heating. In this process, a solid-gas thermal reaction occurs that involves oxidation, sulfation, chlorination, reduction, and pyro hydrolysis.
During roasting, the moisture impurities and non-metals are removed in the form of volatile gas. In our environment sulfides are the major source of air pollution, thereby using this process, they release a large amount of toxic, metallic, and acidic compounds which harm our environment.
Generally roasting is applied for sulfide ores.
In the presence of excess air, a sulfide ore is strongly heated in the presence of air to convert it into a metal oxide. The main motive for applying this process is to remove sulfur in the form of sulfur dioxide and obtain the corresponding metallic oxide.
$2ZnS(s)+3{{O}_{2}}(g)\xrightarrow{{{800}^{{\mathrm O}}}C}2ZnO(s)+2S{{O}_{2}}(g)$
Now, according to the given question, the main function of roasting is to convert the ore into oxide and to remove the volatile matter.

Thus, option (C) is correct.

Note: This roasting process is also used in the food industry. Here this process tries to change the food product by starting various chemical reactions within the food which results in higher availability of particular nutrients, pleasant flavor, and drying of the food product.