The correct option is A >1400 ∘C
In Ellingham’s diagram, the line of the element that lies below can reduce the oxide of the element which lies above it. Therefore, for A to reduce BO2 , the temperature when the line for element A is below that of BO2 according to the graph when T>1400 ∘C,
For T>1400 ∘C,△Gr<0 for A+BO2→B+AO2