among the elements of the main group, the first ionization energy increases\no from left to right across a…

Brief Explanations:

The first - ionization energy is the energy required to remove the outermost electron from a neutral atom in the gaseous state. In the main - group elements, as you move from left to right across a period, the nuclear charge increases while the shielding effect remains relatively constant. This leads to a stronger attraction between the nucleus and the outermost electrons, making it more difficult to remove an electron and thus increasing the first - ionization energy. Moving from right to left across a period decreases the first - ionization energy. As the atomic radius increases (either down a group or due to other factors), the outermost electrons are farther from the nucleus and are easier to remove, so the first - ionization energy decreases. Down a group, the atomic radius increases and the first - ionization energy decreases.

Answer:

A. from left to right across a period.