Answer:. Ca should displace Mn
Explanation:
Calcium is high up in the activity series of metals. Calcium has a very negative redox potential of -2.87 V, next only to potassium. Transition metals of which Manganese is one, does not have such very negative redox potentials so they can easily be displaced by a more highly reactive metal such as Calcium. Elements of group 1 and 2 are very highly reactive.
