Question

which of the following elements has the smallest first ionization energy? a s b o c si d sr e cs

Explanation:

Ionization energy decreases down a group and increases across a period. Among the given elements, Cs (cesium) is in the lowest - left position in the periodic table. It has the largest atomic radius and the outermost electron is the most loosely held among these elements, thus requiring the least energy to remove the first electron.

Answer:

E. Cs