The point of intersection and sudden increase in the slope,in the diagram given below,respectively,indicates

• A
  $ \Delta G = 0 $ and melting or boiling point of the metal oxide
• B
  $ \Delta G > 0 $ and decomposition of the metal oxide
• C
  $ \Delta G < 0 $ and decomposition of the metal oxide
• D
  $ \Delta G = 0 $ and reduction of the metal oxide