In the extraction of copper from its sulphide ore. the metal is finally obtained by the reduction of cuprous oxide with

''Metals are usually not found as nitrates in their ores.'' Out of the following two (I and II) reasons which is/are true for the above observation?
I.  Metal nitrates are highly unstable.
II.  Metal nitrates are highly soluble in water.

The metal oxide which cannot be reduced to metal by carbon is

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