Question

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

Answer 1

Hint: In this process the substance to be purified undergoes thermal decomposition under controlled environment and controlled temperature as well. Carbon dioxide is released as a byproduct.

Complete step by step answer:
-The word calcination means a process where some substance or solid material is heated in a controlled environment and during this temperature is also kept under regulation. This process is done to bring on some changes in the physical or chemical constitution of the substance.
In this process, the ores undergo thermal treatment in the absence or limited supply of air or oxygen, which causes thermal decomposition of the ore. The instrument used here is known as calciner. It is a steel cylinder which can rotate inside a heating furnace to do indirect processing under high temperature within a controlled atmosphere. The temperature can be approximately 550 - 1150$^ \circ C$ or 1000 - 2100$^ \circ F$.
So, for absence or limited supply of oxygen the supply of air is also limited or absent.
-This process is known as calcination because it is mainly used in industries to convert limestone (calcium carbonate: $CaC{O_3}$) into calcium oxide (CaO) and carbon dioxide ($C{O_2}$), this is done to manufacture cement:
                                           $CaC{O_3} \to CaO + C{O_2}(g)$
-This process is done in reactors or furnaces of different types like shaft furnaces, rotary kilns, multiple hearth furnaces or fluidized bed reactors.
-Some examples of calcinations process are:
  (1) Removal of ammonium ions while zeolite synthesis;
  (2) Raw petroleum coke undergoes calcination to decompose volatile components;
  (3) Manufacturing cement by the calcination of limestone;
  (4) To extract rutile from anatase or devitrification of glass materials;
  (5) Bauxite and gypsum undergo calcination to remove the water of crystallisation, etc.
-So, in short, we can say that calcination is the process where metal ore is heated up to high temperatures in the absence or limited supply of air or oxygen. It causes thermal decomposition of calcium ores. It removes water from the ores and gives out carbon dioxide as a byproduct.

So, the correct option is: (C) In the absence of air or limited supply of air.

Note: The controlled temperature we are talking about is taken to be above the thermal decomposition temperature (for decomposition reactions) or the transition temperature (for phase transition reactions). This temperature is usually the one at which the standard Gibbs energy for that particular calcination reaction is zero.