Final answer:
Charlene is in the alarm stage of stress according to Hans Selye's model.
Step-by-step explanation:
According to Hans Selye's general adaptation syndrome model, Charlene is in the alarm stage of stress. The alarm reaction is the body's immediate response to a threatening situation or emergency. In this stage, Charlene's heart racing and flushed face are indicative of the physiological reactions that provide her with the energy to manage the stressor, which in this case is her upcoming solo at the chorus concert. The other stages of stress according to Selye's model are the resistance stage and the exhaustion stage.