If you could create a reactive metal what would it be and how would it react?

Question: If you could create a reactive metal what would it be and how would it react?
- Keywords:
  invention,
  metal,
  quirky
Asked by Mich to Anna, George, Jodi, Rob, Stefan on 13 Nov 2014.
- Stefan Lines answered on 13 Nov 2014:
  
  One which is extremely (explosively) reactive with water like Caesium or Francium!

Question: If you could create a reactive metal what would it be and how would it react?