Answer
See the explanation
Work Step by Step
Across a period (left → right): Ionization energy increases (more protons → stronger nuclear pull).
Down a group (top → bottom): Ionization energy decreases (more electron shells → outer electron farther from nucleus).
Arrange the following elements in order of increasing first ionization energy:
a. \( \mathrm{Rb} < \mathrm{Na} < \mathrm{Be} \)
b. \( \mathrm{Sr} < \mathrm{Se} < \mathrm{Ne} \)
c. \( \mathrm{Fe} < \mathrm{P} < \mathrm{O} \)
