An important oxide ore of iron is

All ores are minerals,but all minerals are not ores,because ....

Pyrolusite is

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.

Litharge $(PbO)$ is an ore/mineral of which element?

Identify the correct pair of minerals and their formulas from the following.