When do we typically become aware that we are forming an impression of another person? when we are under stress. when the information we typically rely on is unavailable or difficult to interpret. when the other person is hostile. when we are feeling hostility toward the person?

The answer is: when the information we typically rely on is unavailable or difficult to interpret.

Impression is the perception or opinion that we have toward other people which we developed by observing other people's behavior

Impression often occurs when we meet new people. The information that we have about new people (such as their personalities or their habit) is unavailable or difficult to interpret. Because of this, we tend to observe their behavior to form an impression toward them.