Final answer:
Option C is correct here, Cs (Cesium) will have the highest ionization energy because it is located at the top-right corner of the periodic table. Oxygen (O) has the highest first ionization energy among the elements provided because it is located at the top right of the periodic table and has a high electronegativity and small atomic radius.
Step-by-step explanation:
The highest first ionization energy typically belongs to elements that are located at the top right of the periodic table, as ionization energy generally increases across a period (left to right) and up a group (bottom to top). For the elements provided (O, Sr, Ba, Cs, Rb), oxygen (O) is situated at the top right relative to the others. Therefore, oxygen (O) is expected to have the highest first ionization energy among the choices given. This is due to its high electronegativity and smaller atomic radius, which makes it harder to remove an electron.
Ionization energy is the energy required to remove an electron from an atom or ion. It is determined by factors such as atomic radius and electron shielding. In general, ionization energy increases across a period from left to right and decreases down a group in the periodic table.
Among the given options, **Cs** (Cesium) will have the highest ionization energy because it is located at the top-right corner of the periodic table, indicating a smaller atomic radius and stronger attraction between the nucleus and the valence electrons.