Question

elements that do not have complete sets of valence electrons tend to *

be simpler.

be smaller.

react.

change from metals to nonmetals.

Explanation:

Elements with incomplete valence electron sets (like most elements except noble gases) tend to react to achieve a stable electron configuration (e.g., octet rule). "Be simpler" and "be smaller" are not related to valence electron completeness. Changing from metal to nonmetal is not a trend of such elements. So the correct option is the one with "react".

Answer:

C. react