Answer: (i),(ii) and (iii)
Roasting causes chemical changes such as oxidation, chlorination, and so on. Impurities are eliminated by the production of volatile oxides.During roasting, moisture and non-metallic impurities in the form of volatile gases are released. Process of roasting consists of solid-gas thermal reaction which includes oxidation, reduction, sulfation, chlorination and pyro hydrolysis. However, roasting which involves sulphides are a major source of air pollution and the main drawback of this process is that it releases a large amount of metallic as well as toxic and acidic compounds which causes harm to the environment.
An example of roasting is when Zinc sulphide is converted into zinc oxide. 2ZnS + 3O2 —> 2ZnO + 2SO2