Question

Which of the following metal oxide are reduced by self reduction method?
A.${\text{C}}{{\text{u}}_2}{\text{O}}$
B.${\text{PbO}}$
C.${\text{HgO}}$
D.${\text{CaO}}$

Answer 1

The elements that do self reduction are mainly the transition metal elements or d block elements. Hence they can be extracted from their ores using a self reduction method.

Complete step by step answer:
As metals that we extract from earth's crust are not pure. In order to get pure metal several steps of metallurgy are as follows: Concentration of ore to remove matrix, concentrated ore to metal oxide by roasting or calcinations, Reduction of metal oxide and Refining.
Conversion of metal in metal oxide can be done in two ways namely roasting and calcination. Roasting is also known as a self reduction method as there is no need to add reducing agents externally. In roasting, heating of ore is done in the presence of air or oxygen below its fusion temperature. It is mainly used for ores having impurities of sulphide. In this impurities are removed in form of volatile oxides.
On the other hand, calcination is done by heating of the ore in the absence of air or oxygen below its fusion temperature. This is mainly done to remove impurities like carbonate, hydroxide and hydrated oxide. In this method, impurities are removed in form of elemental vapour or not in the form of volatile oxides because of absence of oxygen.
During roasting, ${\text{C}}{{\text{u}}_2}{\text{S}}$ converted into ${\text{C}}{{\text{u}}_2}{\text{O}}$ , ${\text{PbS}}$ to ${\text{PbO}}$, ${\text{HgO}}$to ${\text{Hg}}$.
Ore of calcium is converted to ${\text{CaO}}$ by a calcination method.

Thus, the correct options are A, B and C.

Note:
Roasting or self reduction method can be done by both excess and limited supply of air or oxygen. Self reduction method is mainly used for sulphide ores (ex copper, lead, mercury) and calcination mainly used for carbonate ores like calcium.