Adead or weakened pathogen used to establish immunity would most likely be found in?

The choices can be found elsewhere and as follows:

1 a pesticide 
2 an antibiotic 
3 a vaccine
4 a toxin

The correct answer is option 3. A dead or weakened pathogen used to establish immunity would most likely be found in a vaccine. A vaccine typically contains an agent that resembles a disease-causing microorganism and is often made from weakened or killed forms of the microbe, its toxins or one of its surface proteins.