Final answer:
The element with the most negative electron affinity is chlorine (Cl), with an electron affinity of -346 kJ/mol, which is higher than bromine, krypton, potassium, and beryllium.
Step-by-step explanation:
The element with the highest (most negative) electron affinity is chlorine (Cl). Electron affinity refers to the amount of energy released when an electron is added to a neutral atom in the gaseous state to form an anion. The process can be represented as Cl(g) + e- → Cl-(g) and the electron affinity for chlorine is -346 kJ/mol, which is more negative than that of other elements such as bromine (Br), krypton (Kr), potassium (K), and beryllium (Be). Beryllium, in particular, does not form a stable anion and hence has an effective electron affinity of zero or positive value.
In general, the trend for electron affinity in the periodic table shows that electron affinities become less negative as you move down a group due to the increased distance from the nucleus. As you move from left to right across a period, electron affinities tend to become more negative, except for the group 15 elements, which are less negative than expected due to the half-filled p-orbital stability.