WAEC Chemistry 2022 Paper

Concept:Ionization energy depends on how strongly the nucleus attracts the outermost electron.Explanation:Across a period, protons are added to the nucleus while electrons are added to the same principal shell.The inner shell electrons remain nearly constant, so the screening effect does not decrease significantly.Therefore, the effective nuclear charge, $Z_{\mathrm{eff}}$, increases from left to right across the period.A larger $Z_{\mathrm{eff}}$ attracts the outermost electrons more strongly.Thus, removing an electron becomes harder and requires more energy.This directly explains why ionization energy increases across the period.Answer:B. effective nuclear charge increases