Which of the following reactions is an example of autoreduction?

Auto reduction is a process in which sulphide ores of less electropositive metals like Cu, Hg, Pb etc. are heated. In this method, less electropositive metal and a gas – sulphur dioxide
Thus, in simple words we can say the auto reduction process is used in the preparation of less electropositive metals like Cu, Hg, Pb etc.

${\mathrm{Cu}}_{2}\mathrm{O}+\frac{1}{2}{\mathrm{Cu}}_{2}\mathrm{S}\to 3\mathrm{Cu}+\frac{1}{2}{\mathrm{SO}}_{2}$
This reaction includes reduction of copper (l) oxide by copper(l) sulphide. in this process, copper is reduced by itself hence this process is known as autoreduction and the solidified copper. So, obtained is known as blister copper.