Question

question 10 of 10
which of the following elements has the lowest first ionization energy?

a. oxygen (o)

b. strontium (sr)

c. scandium (sc)

d. phosphorus (p)

Explanation:

First ionization energy generally decreases down a group and increases across a period (with some exceptions). Strontium (Sr) is in Group 2, Period 5. Oxygen (O) is in Group 16, Period 2; Phosphorus (P) is in Group 15, Period 3; Scandium (Sc) is in Group 3, Period 4. Down a group, the atomic radius increases, so the outermost electron is farther from the nucleus and easier to remove. Sr is lower in the periodic table (larger atomic radius) compared to the others, so it has the lowest first ionization energy.

Answer:

B. Strontium (Sr)