The element with the highest ionization energy is

The element with the highest ionization energy is Helium due to its duplet stable electronic configuration.

What is Ionization Energy?

Ionization energy is the amount of energy required to remove an electron from an atom in its gaseous state. The higher the ionization energy, the more difficult it is to remove an electron.

Helium’s Position on the Periodic Table

• Helium is a noble gas, located in Group 18, Period 1 of the periodic table.
• It has a full electron shell (2 electrons), making it extremely stable.
• The atomic radius of helium is very small, and its electrons are held tightly by the nucleus due to the high effective nuclear charge. This makes it difficult to remove an electron from helium.

Why Helium Has the Highest Ionization Energy:

• Helium has the highest effective nuclear charge among all elements. The nucleus attracts the two electrons very strongly, and because it has only two electrons in a small electron shell, it is energetically unfavorable to remove one.
• This strong attraction results in a high ionization energy.

Why Not Other Options?

• Option A (Oxygen): While oxygen has a relatively high ionization energy, it is still much lower than that of helium. Oxygen is in Period 2, but it has more electron shielding and a larger atomic radius compared to helium.
• Option B (Nitrogen): Nitrogen, like oxygen, has a high ionization energy, but it is still less than that of helium. Its atomic radius is larger, and its electrons are more shielded.
• Option D (Carbon): Carbon's ionization energy is also high but lower than that of helium. Carbon's atomic radius is larger, and its electrons are not as tightly held as those in helium.

Conclusion

Due to helium's small size and high effective nuclear charge, it has the highest ionization energy of all elements. Therefore, the correct answer is Option C (Helium).