Calcination is the process of heating the ore:

The role of calcination in metallurgical operations is

The reaction that does not define calcination is:

Roasting of sulphides gives the gas $X$ as a byproduct. This is a colourless gas with a choking smell of burnt sulphur and causes great damage to respiratory organs as a result of acid rain. Its aqueous solution is acidic,acts as a reducing agent,and its acid has never been isolated.
The gas $X$ is

Roasting is generally done in case of the following:

The mixture obtained from the roasting of copper pyrites is ......... .