Which of the following atoms has the highest first ionization energy, making it the most difficult to remove an electron?

• A. Ne (Neon)
• B. K (Potassium)
• C. Na (Sodium)
• D. Li (Lithium)

Answer: (A)

Verified step by step guidance

1. Understand that the first ionization energy is the energy required to remove the outermost electron from a neutral atom in the gas phase.
2. Recall that ionization energy generally increases across a period (left to right) in the periodic table because the nuclear charge increases, pulling electrons closer and making them harder to remove.
3. Recall that ionization energy generally decreases down a group (top to bottom) because electrons are farther from the nucleus and are shielded by inner electrons, making them easier to remove.
4. Identify the positions of the given elements: Li, Na, and K are all in Group 1 (alkali metals) and increase in atomic number down the group, while Ne is a noble gas at the end of the same period as Li.
5. Conclude that Neon (Ne), being a noble gas with a full valence shell and located at the far right of the period, has the highest first ionization energy among the options, making it the most difficult to remove an electron.