Question

no one realizes¹ realize² the effects he or she has on another until its nearly too late.
option 1: realizes
option 2: realize

Explanation:

The subject "no one" is a singular indefinite pronoun, so the verb should be in the singular form. "realizes" is the singular form of the verb "realize" for the third - person singular subject "no one", while "realize" is the base form used for plural subjects or with modal verbs, etc. So the correct option is Option 1: realizes.

Answer:

Option 1: realizes