Final answer:
The correct answer is C, as electronegativity decreases with an increase in atomic size because electrons are more attracted to the nucleus of smaller atoms.
Step-by-step explanation:
In general, electronegativity decreases as atomic size increases because a shared electron pair is closer to the nucleus of a smaller atom, which therefore attracts these electrons more strongly. The correct answer to the student's question is 'C. decreases; more; increase; decrease'. This is due to the fact that as atoms increase in size going down a group on the periodic table, the outer electrons are further away from the nucleus and more shielded by inner shell electrons, thus reducing the atom's ability to attract electrons within a bond.
Furthermore, an increase in atomic size typically indicates an increase in the principal quantum number (larger orbitals), which also contributes to a decrease in electronegativity. This illustrates a key periodic trend: electronegativity decreases from top to bottom within a group because of the increased distance between the nucleus and the bonding pair of electrons, making the nucleus less effective at attracting the bonding electrons.