In Pavlov's experiments, which of the following was used as a stimulus for development of an acquired reflex?

Options

A. Food
B. Smell of food
C. Sound of bell
D. Both (1) and (2)

Answer

To solve the question regarding Pavlov's experiments and the stimulus used for the development of an acquired reflex, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Concept of Classical Conditioning**:
- Pavlov's experiments are foundational in the study of classical conditioning, which involves learning through association. A neutral stimulus becomes associated with an unconditioned stimulus to elicit a conditioned response.

2. **Identify the Components of Pavlov's Experiment**:
- In Pavlov's experiment, he used a dog as the subject. The unconditioned stimulus (US) was food, which naturally elicited a response (salivation). The neutral stimulus (NS) was the sound of a bell.

3. **Recognize the Role of the Bell**:
- Initially, the bell did not cause any salivation. However, after repeated pairings of the bell (NS) with the food (US), the dog began to salivate in response to the bell alone. This demonstrates that the bell became a conditioned stimulus (CS).

4. **Evaluate the Options Given**:
- A) Food: This is the unconditioned stimulus.
- B) Smell of food: This is also an unconditioned stimulus that can elicit a natural response.
- C) Sound of bell: This is the conditioned stimulus that was developed through the experiment.
- D) Both 1 & 2: This option suggests that both food and the smell of food were used as stimuli for the acquired reflex.

5. **Determine the Correct Answer**:
- The question asks specifically for the stimulus used for the development of an acquired reflex. The sound of the bell is the correct answer because it is the neutral stimulus that became conditioned through the process of classical conditioning.

### Final Answer:
- The correct answer is **C) Sound of bell**.