Final answer:
The unconditioned stimulus in Idu's experience is becoming ill with food poisoning. This is because the illness is what naturally caused the queasy feeling without any prior learning, which is central to classical conditioning and taste aversion.
Step-by-step explanation:
In the example provided, Idu ate a bad batch of clam chowder and became ill with food poisoning. Now, even the smell of clam chowder can make him feel queasy. To answer the question, the unconditioned stimulus is B) Becoming ill with food poisoning. In classical conditioning, an unconditioned stimulus is something that naturally and automatically triggers a response without any learning involved. Thus, the illness Idu experienced is the unconditioned stimulus because it naturally caused him to feel queasy, which is the unconditioned response. The smell of clam chowder becomes a conditioned stimulus after being associated with the unpleasant experience of food poisoning.
This phenomenon is related to taste aversion, a type of conditioning in which an organism learns to avoid a food that has made them ill. Classic research by Garcia and Koelling supports the idea that this type of learning can occur even when there is a long delay between eating the food (the conditioned stimulus) and feeling ill (the unconditioned stimulus), which is relevant to both survival and medical treatments.