Answer:
unconditioned Stimulus
Explanation:
Pavlov's classical conditioning experiments result in getting a reaction from the unconditioned stimulus which was earlier triggered by a neutral stimulus. Pavlov's noticed that dog secrets saliva on viewing the food attender and it inspired him to conduct the experiment. Then he arranged a bell in the hall and the bell was rung each time when the attendant arrived. Later the result was that the neutral stimulus food was replaced by the unconditioned stimulus (bell) and reaction (saliva) was obtained.