Roasting involves
(A) Only volatilization of volatile impurities
(B) Only volatilization of volatile impurities and decomposition of the ore
(C) Volatilization of volatile impurities and decomposition and oxidation of the ore
(D) Oxidation and reduction of the ore and slag formation

Hint: In the metallurgical process of roasting, ore is heated below its melting point in the presence of excess air and converted into its oxide. Sulfide-based roasting is a major source of air pollution, and it has the further disadvantage of releasing great amounts of acidic, poisonous, and metallic chemicals into the environment. In metallurgical processes, when ores are transformed into oxides and then metals are extracted, roasting is used.

Complete Step by Step Answer:
Non-metallic and moisture impurities are released as volatile gases during roasting. The solid-gas thermal reaction, which includes reduction, oxidation, chlorination, sulfation, and pyro hydrolysis, occurs during the roasting process.

Volatile substances, moisture, and impurities are all eliminated throughout this process. There is no dehydration step in the roasting process. An example of a roasting process is the conversion of zinc sulphide into zinc oxide.
$2ZnS+3O_2 \rightarrow 2ZnO + 2SO_2$
Correct Option: (C) Volatilization of volatile impurities and decomposition and oxidation of the ore.

Additional Information: The process of roasting has many advantages. The substances that have been roasted can easily be powdered. It is a very quick method and requires very little fat. The content of moisture in the substances that have been roasted, gets reduced.

Note: Typically, roasting is carried out to ensure that the desired chemical reaction begins slowly, continues for a sufficient amount of time to transform enough of the product's chemicals into the desirable material, and then ends. Roasting is an exothermic process.