Which of the following atoms in the ground state requires the least amount of energy to remove its valence electron?

• A. Na
• B. Mg
• C. Ca
• D. K

Answer: (D)

Verified step by step guidance

1. Identify the elements given in the problem and their positions in the periodic table: Na (Sodium), Mg (Magnesium), Ca (Calcium), and K (Potassium).
2. Recall that the energy required to remove a valence electron is called the ionization energy, which generally decreases as you move down a group in the periodic table because the valence electron is farther from the nucleus and more shielded by inner electrons.
3. Compare the group and period of each element: Na and Mg are in period 3, Ca and K are in period 4, with K being in group 1 (alkali metals), Na also in group 1, Mg in group 2, and Ca in group 2.
4. Understand that elements in group 1 have lower ionization energies than those in group 2 because group 1 elements have only one valence electron, which is easier to remove.
5. Conclude that among the listed atoms, K (Potassium), being in group 1 and period 4, has the lowest ionization energy due to its larger atomic radius and weaker attraction to its valence electron, thus requiring the least energy to remove it.