The term TYPE OF REACTION can refer to four different types of reactions: CHAIN, GUT, NUCLEAR, and kneejerk. CHAIN reactions involve a series of chemical reactions that occur in a sequence, with each reaction triggering the next. GUT reactions are instinctive responses to a situation or stimulus, often without conscious thought. NUCLEAR reactions involve the transformation of one element into another through the release or absorption of energy. Kneejerk reactions are quick, often impulsive responses to a situation or stimulus.