In calcination,the ore is heated in $......$.

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

In metallurgy,calcination is used for .........

In the extraction of iron from hematite,what is the role of limestone?

The process of heating an ore in the presence of excess air to a temperature below its melting point is called:

$A$ metal obtained directly by roasting of its sulphide ore is