Answer:
Lowest ionization energy: Cs
Most favorable electron affinity: Cl
Most energy required to remove an electron: Cu2+
Explanation:
Ionization energy decreases down the group. That means that as we move down the group, the ionization energy of elements decreases due to greater distance of the outermost electron from the nucleus and greater screening effect of inner electrons on this outermost electron. Hence Cs has the lowest ionization energy.
Electron affinity of halogens decreases down the group. Hence, Cl possess the most favorable electron affinity.
When an electron has been removed from an atom, the removal of the next electron is usually harder. Thus, the second ionization energy is always greater than the first ionization energy and so on. Thus, it is most difficult to remove an electron from Cu^2+ from which two electrons have already been removed.
