Between Cl and Cl^-, which one do you expect to have a more positive electron affinity?

The electron affinity increases as you go up a group. As an example, S has a higher electron affinity than Se. However, O which is above S has a lower electron affinity than S. 

What is the reason for this phenomenon? 

Arrange the following elements from most negative to most positive electron affinity values.

Which member of the halogen group has the lowest electron affinity?