Step-by-step explanation:
The correct option to complete the sentence "s'intéresser _______ (to be interested in)" is Option 2: à.
The sentence can be translated as "to be interested in" and in French, the preposition "à" is used after the reflexive verb "s'intéresser" to introduce the object or topic of interest. Therefore, the correct option is "à" which corresponds to "in" in English.