Question

which of the following elements has the smallest first ionization energy?

Explanation:

First ionization energy decreases down a group and increases across a period (left - to - right). Among the given elements \(S\) (sulfur), \(O\) (oxygen), \(Si\) (silicon), \(Sn\) (tin), and \(C\) (carbon):

• \(O\) and \(C\) are in period 2, \(S\) and \(Si\) are in period 3, and \(Sn\) is in period 5.
• Since \(Sn\) is in the lowest period (period 5) among them, it has the largest atomic radius (due to more electron shells) among these elements. Larger atomic radius means the outermost electrons are more shielded from the nucleus and easier to remove.

Answer:

D. \(Sn\)