Definition: In this task, you are given a multiple-choice question about healthcare. Answer the question based on your information and classify your answers into '1', '2', '3', and '4'.
Input: Question: The arenio ion is a reaction intermediate that is formed in the reactions of: 
 Options:  <1> Electrophilic addition. <2> Electrophilic aromatic substitution. <3> Nucleophilic substitution. <4> Nucleophilic addition. <5> Aromatic nucleophilic substitution.
