Question

of the following elements, which one has the smallest first ionization energy? carbon silicon boron aluminum

Explanation:

Ionization energy generally increases across a period (from left to right) and decreases down a group in the periodic table. Carbon (C) is in period 2, group 14; silicon (Si) is in period 3, group 14; boron (B) is in period 2, group 13; aluminum (Al) is in period 3, group 13. Comparing these, Al is further down the group (lower ionization energy than B) and further to the left (lower ionization energy than Si and C).

Answer:

aluminum