Which of the following statement is correct based on Ellingham diagram.                  

In Ellingham’s diagram, a graph is plotted between ${\Delta }_{\text{f}}^{\text{0}}\text{G}$ of oxide (y-axis) Vs temperature (T) ( x - axis )

A) A metal whose ${\Delta }_{\text{f}}^{\text{0}}\text{G}$ of  oxide is more negative acts like a reducing agent to the other metal oxide whose ${\Delta }_{\text{f}}^{\text{0}}\text{G}$ of oxide is less negative${\Delta }^0\text{G}$;of the net reaction will be negative. 

Ex:    ${\text{2Cu}}_{\text{(s)}}+{\text{O}}_{\text{2}}\text{(g)}\to {\text{Cu}}_{\text{2}}\text{O(s) ; }{\Delta }_{\text{f}}^{\text{0}}\text{G}=\text{less}-\text{ve;}$     … (1) 

         ${\text{2Mg}}_{\text{(s)}}+{\text{O}}_{\text{2}}\text{(g)}\to \text{MgO(s) ; }{\Delta }_{\text{f}}^{\text{0}}\text{G}=\text{more}-\text{ve;}$  … (2)

         Equation (2) – Equation (1) 

         $\text{2Mg(s)}-{\text{Cu}}_{\text{2}}\text{O(s)}\to \text{2MgO(s) + 2Cu(s); }{\Delta }^{\text{0}}\text{G}=-\text{ve}$

         Thus ‘Mg’ can reduce Cu₂O;

B) At certain temperature ${\Delta }_{\text{f}}^{\text{0}}\text{G}$ formation of a metal oxide becomes positive. It indicates that above that temperature the metal oxide decomposes to metal and oxygen. 

         Ex: At about  500° C the ${\Delta }_{\text{f}}^{\text{0}}\text{G}$ of HgO and Ag₂O becomes positive. 

C) For certain metals like Zn and Mg in their ${\Delta }_{\text{f}}^{\text{0}}\text{G}$ Vs T plot a sudden abrupt increase in ${\Delta }_{\text{f}}^{\text{0}}\text{G}$ is observed this indicates melting of metal oxide.