The correct option is B Thermal reduction
Ellingham diagram is the graph between ΔG and T of various oxides. These help in predicting the feasibility of thermal reduction of ores. The stability of the oxides as a function of temperature can be obtained from the position of the line for a given reaction on the Ellingham diagram. Reactions closer to the top of the diagram are the most "noble" metals (for example, gold and platinum), and their oxides are unstable and easily reduced. As we move down toward the bottom of the diagram, the metals become progressively more reactive and their oxides become harder to reduce.