In this task, you are given a question and answer options for that question. Using this information, you have to classify each text into different topics: medicine, nursery, psychology, chemistry, pharmacology, biology.

Question: About free radicals: 
 Options:  <0> They are compounds that contain two or three unpaired electrons in an outer orbital. <1> Reactive oxygen species (ROS) in the cell are only generated enzymatically. <2> Hydrogen peroxide is the most damaging radical in the cell. <3> The hydroxyl radical originates non-enzymatically (Heber-Weiss reaction) and damages proteins and DNA. <4> Oxygen is a triradical.
chemistry

Question: A rat pathogen that has fleas as vectors of transmission to humans is: 
 Options:  <0> Rickettsia rickettsii. <1> Yersinia pestis <2> Borrelia burgdorferi. <3> Ehrlichia ewingii. <4> Brucella abortus.
biology

Question: According to the Arrhenius equation (k = A e-Ea / RT): 
 Options:  <0> The speed of a reaction is directly proportional to the temperature. <1> A high activation energy implies that the speed constant depends markedly on the temperature. <2> The pre-exponential factor or frequency factor (A) is dimensionless. <3> The activation energy depends on the temperature. <4> The activation energy is always negative.

pharmacology