Which element has greater electron affinity and why

1- Cl or Br, why?

2- O or F, why?

3- Na or Si, why?

4- K or Na, why?

1 Cl down the group electro negativity decreases in 17th group with fluorine as exception

2 O because of its small size the incoming electron experiences more repulsion in F

3 Si because Na is a metal and metals have low electron affinity

4 Na because down the group metallic character increases