Some of the possible limitations of the Thermodynamic arguments about Ellingham diagram is/are given below. Choose the ones that are genuine limitations (for Thermodynamic arguments based on Ellingham Diagram):
The theory assumes (often incorrectly) that the reactants and products are in equilibrium
Although the Ellingham diagram predicts the feasibility of the reaction, it does not give any data regarding competing alternative reactions
Also the Ellingham diagram does not predict the rates of the reactions
Options a c and d are well known drawbacks of the theory behind Ellingham diagram.
Although Ellingham diagram gives us a good idea as to which reducing agent to choose at a particular temperature, the underlying idea assumes the system to be in chemical equilibrium. Often there are solid reactants and products and in many cases such equilibrium is never reached.
Thermodynamic feasibility also does not reveal anything about the rate of the reactions. In principle, a particular reaction may be possible but it might take too long to be profitable! Economic factors are very important in metallurgy. Additionally, these compelling arguments do not offer insights into other more favuorable competing reactions!