In isolation of which one of the following metals from their ores, the use of cyanide salt is not commonly involved ?

On heating quick lime with coke in an electric furnace, we get

Roasting of sulphides gives the gas $X$ as a byproduct. This is a colourless gas with 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

Which of the following pairs of metals is purified by van Arkel method?

Correct match is