Which of the following elements has the lowest ionization energy?

• A. Al
• B. K
• C. Mg
• D. Na

Answer: (B)

Verified step by step guidance

1. Understand that ionization energy is the amount of energy required to remove an electron from a gaseous atom or ion. Elements with lower ionization energy lose electrons more easily.
2. Recall the general trend of ionization energy in the periodic table: it increases across a period (left to right) and decreases down a group (top to bottom).
3. Identify the positions of the given elements on the periodic table: K (potassium) and Na (sodium) are in Group 1 (alkali metals), Mg (magnesium) and Al (aluminum) are in Period 3 but in Groups 2 and 13 respectively.
4. Since ionization energy decreases down a group, potassium (K), which is below sodium (Na) in Group 1, will have a lower ionization energy than sodium.
5. Compare potassium with magnesium and aluminum, which are in the same period but to the right of potassium; elements to the right generally have higher ionization energies, so potassium has the lowest ionization energy among the options.