Final answer:
Oxygen (O) will have the highest first ionization energy out of the given elements because ionization energy increases across a period and decreases down a group in the periodic table, and oxygen is in the second period to the far right.
Step-by-step explanation:
The student's question, “Which atom will have the highest ionization energy: O, Sr, Ba, Cs, or Rn?” can be answered using our knowledge of the periodic table. Ionization energy tends to increase across a period from left to right and decrease down a group. This means that among the given elements, oxygen (O), being in the second period and to the right, is expected to have the highest first ionization energy.
For a more in-depth understanding:
- The noble gas radon (Rn), despite being far to the right, is much lower in the periodic table compared to oxygen, and thus, it has a lower ionization energy.
- The alkali metal cesium (Cs) and the alkaline earth metals strontium (Sr) and barium (Ba) are all further down the periodic table and to the left compared to oxygen, meaning they have much lower ionization energies as well.
Therefore, Oxygen (O) will have the highest ionization energy out of the options given.