Copper is the most noble of the first row transition metals and occurs in small deposits in several countries. Ores of copper include chalcanthite $\left(\mathrm{CuSO}_4 \cdot 5 \mathrm{H}_2 \mathrm{O}\right)$, atacamite $\left(\mathrm{Cu}_2 \mathrm{Cl}(\mathrm{OH})_3\right)$, cuprite $\left(\mathrm{Cu}_2 \mathrm{O}\right)$, copper glance $\left(\mathrm{Cu}_2 \mathrm{~S}\right)$ and malachite $\left(\mathrm{Cu}_2(\mathrm{OH})_2 \mathrm{CO}_3\right)$. However, $80 \%$ of the world copper production comes from the ore of chalcopyrite $\left(\mathrm{CuFeS}_2\right)$. The extraction of copper from chalcopyrite involves partial roasting, removal of iron and self-reduction.
In self-reduction, the reducing species is