Question

Auto reduction process is used in the extraction of:
A.Cu and Pb
B.Zn and Hg
C.Cu and Al
D.Fe and Pb

Answer 1

Auto reduction process is a widely used industrial process of metal extraction from minerals or ores especially for less electropositive metals like copper (Cu), lead (Pb), mercury (Hg) etc.

Complete step by step answer:
Auto reduction is a process in which sulphide ores of less electropositive metals like Cu, Hg, Pb etc. are heated in presence of air. It is done for the conversion of the ore into sulphate or oxide, which then reacts with the remaining ore of the sulphate in the absence of air to give the 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.
Some of the examples are as following,
Copper (Cu) ore extraction: Here, partial roasting of sulphide ore of Cu to give the oxide. After some time, air supply is stopped and the temperature is raised to complete the leftover sulphide ore to form the metal.
$2C{{u}_{2}}S+3{{O}_{2}}\to 2CuO+2S{{O}_{2}}$
$C{{u}_{2}}S+2C{{u}_{2}}O\to 6Cu+S{{O}_{2}}$
Lead (Pb) ore extraction:
$2PbS+3{{O}_{2}}\to 2PbO+2S{{O}_{2}}$
$2PbO+PbS\to 3Pb+S{{O}_{2}}$
Mercury (Hg) ore extraction:
$2HgS+3{{O}_{2}}\to 2HgO+2S{{O}_{2}}$
$2HgO+HgS\to 3Hg+S{{O}_{2}}$

So, here the correct answer will be option A. Cu and Pb.

Note:
Remind the less electropositive metals like Cu, Hg, Pb metals are extracted by the auto-reduction method. There is no external reducing agent used in this process, for this reason the process is termed as “Auto-reduction”. There are two steps of the auto-reduction process, the first includes heating with air, and the last part includes heating without air and finally gives metal from the mineral ore.