Which of the following is not true in regard to atomic radii of main group elements? a. atomic radii generally increase as you move down a group. b. atomic radii generally increase as you move from left to right across a period. c. atomic radii size is related to the number of electrons in the valence level and the number of protons in the nucleus. d. atomic radii decrease in size when the pull of electrons toward the nucleus of an atom is greater.

B. Atomic radii generally increase as you move from left to right across a period.

On moving down a group, the nuclear charge increases but electrons are being added to new shells and the effect of addition of new shells is more pronounced, thus the valence electrons move far from the nucleus, the atomic radii increase.

On moving across a period, the nuclear charge increases but electrons are being added to same shells and the effect of nuclear charge is more pronounced, thus the valence electrons are being tightly held by the nucleus, the atomic radii decrease.