Calcination is the process of heating the ore: (A) In inert gas (B) In the presence of air (C) In the absence of air or limited supply of air (D) In the presence of CaO and MgO

Calcination is a thermal treatment process used primarily in metallurgy and chemistry. To solve the question, let's analyze the options provided for the calcination process:

Definition of Calcination:
Calcination is the process of heating an ore (usually a metal ore) to a high temperature in the absence of air or in a limited supply of air. This process is typically used to remove volatile substances, such as water, carbon dioxide, or other gases, from the ore. It can also convert metal carbonates into oxides by driving off carbon dioxide.

Explanation of Each Option:
(A) In inert gas:

This is not correct because calcination specifically requires the absence of reactive gases, which is not the same as being in an inert gas atmosphere.
(B) In the presence of air:

This is also incorrect, as calcination does not involve heating in the presence of a sufficient amount of air. Heating in the presence of air can lead to oxidation, which is not the goal of calcination.
(C) In the absence of air or limited supply of air:

This is the correct answer. Calcination is performed in the absence of air or with limited air to avoid unwanted reactions, like oxidation.
(D) In the presence of CaO and MgO:

This option is incorrect. While CaO (calcium oxide) and MgO (magnesium oxide) can be involved in other processes, calcination specifically does not require these substances.
Conclusion:
The correct answer is (C) In the absence of air or limited supply of air. This option accurately reflects the conditions under which calcination occurs, focusing on the removal of volatile materials and the transformation of certain compounds.