among the elements of the main group, the first ionization energy increases from left to right across a…

Brief Explanations:

The first - ionization energy is the energy required to remove the out - most 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. As you move down a group, the atomic radius increases, the outermost electrons are farther from the nucleus and more shielded, so the first - ionization energy decreases. Also, an increase in atomic radius generally leads to a decrease in first - ionization energy.

Answer:

A. from left to right across a period.