Please answer my chemistry question below?

If you are looking for the more exothermic electron affinity then you are looking for the more positive, not negative value. With that being said, the general trend for electron affinity increases from left to right across a row (as you move right elements are increasingly wanting electrons to fill their valence shells to become more stable) and from bottom to top across a column (atoms towards the bottom of a column have larger shell sizes so the entering electron is farther from the nucleus resulting in a less effective nuclear charge). Now, with the trend explained, Magnesium has a more positive electron affinity than sulfur, and potassium has a more positive electron affinity than cesium. Hope this helps.