Which of the following elements has the lowest ionization energy?

• A. Na
• B. Mg
• C. Al
• D. Cl

Answer: (A)

Verified step by step guidance

1. Understand that ionization energy is the 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 in the periodic table: Na (Sodium) is in Group 1, Period 3; Mg (Magnesium) is in Group 2, Period 3; Al (Aluminum) is in Group 13, Period 3; Cl (Chlorine) is in Group 17, Period 3.
4. Since all elements are in the same period, compare their ionization energies based on their group number. Ionization energy generally increases from left to right across a period, so elements on the left have lower ionization energies.
5. Conclude that Sodium (Na), being the furthest to the left in Period 3 among the options, has the lowest ionization energy.