Based on periodic trends, which one of the following elements do you expect to be most easily reduced? Ca,Sr,Cl,or P?
The most easily reduced metal should be the RIGHTMOST element on the Periodic Table, i.e the element with the GREATEST nuclear charge, and that is chlorine.
We consider the reaction:
Now electron affinity measures this process precisely (as long as the element is in the gaseous state!). So, we should look up a Table of Electron Affinities. Is this consistent with what we have argued?