Question

elements that do not have complete sets of valence electrons tend to *
1 point
be simpler.
be smaller.
react.
change from metals to nonmetals.

Explanation:

Elements with incomplete valence electron sets aim to achieve a stable electron configuration (like a noble gas configuration). This drives them to react (e.g., form bonds, gain/lose electrons) to complete their valence shells. "Be simpler" and "be smaller" are not related to valence electron completeness. Changing from metals to nonmetals also doesn't relate to this concept. So the correct choice is the one about reacting.

Answer:

C. react.