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? 

• A. O having a much smaller radius causes the electron affinity to be less exothermic because of the repulsive forces between the electrons
• B. O having much fewer protons causes the electron affinity to be less exothermic because of the repulsive forces between the protons
• C. O having a much smaller nucleus causes the electron affinity to be less endothermic because of the attractive forces between the electrons
• D. O having much fewer electrons causes the electron affinity to be less endothermic because of the attractive forces between the electrons

Answer: (A)