Select the correct statements (Ellingham diagram):

• A

  When temperature is raised, a point will be reached where the graph crosses the ${\mathrm{Δ}}_{\mathrm{f}}{\mathrm{G}}^0=0$ line. Below this temperature, the free energy of formation of the oxide is negative, so the oxide is stable.

• B

  When the temperature is raised, d point will be reached where the graph crosses the ${\mathrm{Δ}}_{\mathrm{f}}{\mathrm{G}}^0=0$ line. Above this temperature, the free energy of formation of the oxide is positive, and the oxide becomes unstable, and should decompose into the metal and dioxygen.

• C

  Theoretically, all oxides can be decomposed to give the metal and dioxygen if a sufficiently high temperature can be attained.

• D

  Theoretically, all oxides cannot be decomposed to give the metal and dioxygen if a sufficiently high temperature can be attained.