What trend is observed in ionization energy as you move down a group in the periodic table?

As you move down a group in the periodic table, there is a clear trend where ionization energy decreases. This is primarily due to two key factors: the increase in atomic size and the effect of electron shielding.

As you go down a group, each successive element has an additional electron shell compared to the one above it. This increase in the number of shells causes the outermost electrons to be farther away from the nucleus. Consequently, the attraction between these outer electrons and the positively charged nucleus becomes weaker because of the increased distance.

Moreover, the inner shell electrons provide a shielding effect, which partially blocks the positive charge of the nucleus from reaching the outer electrons. This means that the outermost electrons feel less effective nuclear charge, making them easier to remove. As a result, the ionization energy—the energy required to remove an electron from an atom—decreases down a group.

This trend is consistent across the periodic table, with the general observation that moving from the top of a group to the bottom leads to lower ionization energies. Thus, the answer indicating that ionization energy decreases as you move down a group in the periodic table is indeed correct.