In ________ conditioning, the unconditioned stimulus unconditionally elicits a reaction. For example, a bit of black pepper blown into the eye produces a blinking response.

According to the theory of Classical Conditioning, an Unconditional Stimulus can be defined as such a stimulus that is capable of triggering a response spontaneously and naturally without the requirement of a previous learning or knowledge about the stimulus.
A Neutral stimulus can be defined as such a stimulus which is responsible for drawing or focusing the attention of a person to a particular event.
A Conditional Stimulus can be defined as such a stimulus which is generated due to the repeated integration of an Unconditional stimulus to a Neutral stimulus. The repeated integration eventually results in the generation of a conditioned response.
In the given example, a bit of black pepper blown into the eyes for the first time is an example of unconditional stimulus. This stimulus initiates a spontaneous or unconditional response, that is, blinking of eyes.
But, when this unconditional stimulus gets integrated to the neutral stimulus (irritation in the eyes draws the attention of the person) repeatedly, it can result in the generation of a Conditioned Response (blinking of eyes whenever any foreign object gets into it).