Answer
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Work Step by Step
As we move across a row of the periodic table, electrons are added to the same energy level (valence shell), resulting in an increase in effective nuclear charge. This increase in positive charge attracts the electrons more strongly, requiring more energy to remove them, leading to the increase in ionization energy.
In contrast, as we move down a column, electrons are added to higher energy levels (higher shells), resulting in increased electron shielding and a decrease in effective nuclear charge. This reduced positive charge leads to weaker attraction between the nucleus and outermost electrons, making it easier to remove them, resulting in the decrease in ionization energy.
