Which property of transition metals enables them to behave as catalysts?

In the two tetrahedral structures of dichromate ion

1 mole of liquid A and 2 moles of liquid $$B$$ make a solution having a total vapour pressure 40 torr. The vapour pressure of pure $$A$$ and pure $$B$$ are 45 torr and 30 torr respectively. The above solution

Which of the following would not be a good choice for reducing nitrobenzene to aniline?