Final answer:
Sulfur (S), Na+, Chlorine (Cl), and Aluminum (Al) are the atoms/ion identified in each of the cases mentioned.
Step-by-step explanation:
1. An atom larger than P is Sulfur (S). The atomic radius generally increases as you move down a group in the periodic table.
2. An ion smaller than K+ is Na+ (Sodium ion). When an atom loses an electron to become a cation, its radius decreases.
3. An atom with higher electron affinity than S is Cl (Chlorine). Electron affinity is the energy released when an electron is added to a neutral atom.
4. An atom with a lower first ionization energy than Ga is Al (Aluminum). Atomic radius and shielding effect are factors that affect the ionization energy.