Arrange the following elements in order of increasing first ionization energy: Na, Mg, Al, Si.

• A. Al < Si < Na < Mg
• B. Si < Al < Mg < Na
• C. Na < Mg < Al < Si
• D. Mg < Na < Si < Al

Answer: (C)

Verified step by step guidance

1. Recall that the first ionization energy is the energy required to remove one mole of electrons from one mole of gaseous atoms. It generally increases across a period (left to right) in the periodic table due to increasing nuclear charge and decreases down a group due to increasing atomic radius and electron shielding.
2. Identify the position of each element (Na, Mg, Al, Si) in the periodic table. All four elements are in the same period (Period 3), with Na on the far left and Si more to the right.
3. Understand that as you move from left to right across Period 3, the first ionization energy generally increases because the effective nuclear charge increases, pulling electrons closer and making them harder to remove.
4. Arrange the elements in order of increasing first ionization energy based on their position: Sodium (Na) has the lowest ionization energy, followed by Magnesium (Mg), then Aluminum (Al), and Silicon (Si) has the highest among these four.
5. Therefore, the correct order of increasing first ionization energy is: \(\mathrm{Na} < \mathrm{Mg} < \mathrm{Al} < \mathrm{Si}\).