Which one of the following is an emotion?

The correct option is Fear.

Understanding Emotions vs. Cognitive Processes and Stimuli:

1. Fear: Fear is a fundamental, intense emotion triggered by the perception of danger, threat, or harm. It involves both psychological reactions (feeling scared or anxious) and physiological responses (such as an increased heart rate and the release of adrenaline).

2. Memory: Memory is a cognitive function or process involving the encoding, storage, and retrieval of information, not an emotion.

3. Attention: Attention is the cognitive process of selectively focusing on a discrete aspect of information while ignoring other perceivable information.

4. Stimulus: A stimulus is any event, object, or sensory input from the environment that evokes a functional response in an organism.

Therefore, among the given choices, Fear is the only emotion.