Which of the following describes ionization energy across a period from left to right?

Ionization energy is the amount of energy required to remove an electron from an atom in its gaseous state. As you move across a period from left to right on the periodic table, the ionization energy tends to increase. This trend occurs due to several reasons.

First, as you move across a period, the number of protons in the nucleus increases, which leads to a greater positive charge. This increases the attractive force between the nucleus and the electrons. As a result, it requires more energy to remove an electron from the atom.

Second, although electrons are being added to the same energy level as you move from left to right, the effective nuclear charge experienced by the outermost electrons increases. This means the electrons are held more tightly by the nucleus, contributing to the increase in ionization energy.

In conclusion, as you move from left to right across a period, the trend of increasing ionization energy reflects the combined effects of increased nuclear charge and effective nuclear attraction on the valence electrons.