Question

which of the following elements has the smallest first ionization energy?
incorrect, 3 attempts remaining
a s
b o
c si
d sr
e cs
ionization generally increases across a period and decreases down a group. while strontium would have a fairly low first ionization, it is not the least of these choices.

Explanation:

Ionization energy generally increases across a period and decreases down a group. Cesium (Cs) is in Group 1 (alkali metals) and is lower in the group compared to the other elements. Strontium (Sr) is in Group 2. Sulfur (S), oxygen (O), and silicon (Si) are in higher - group numbers. Since ionization energy decreases down a group, Cs, being a Group 1 element and lower in the group compared to the others (Sr is in Group 2, S, O, Si are in higher groups), will have the smallest first ionization energy.

Answer:

E. Cs