The answer is alarm reaction.
The resistance phase is the second stage of the general adaptation syndrome (GAS), where the body attempts to resist or adapt to the stressor. During this phase, the body remains on high alert, and physiological responses are sustained to cope with the stress. However, this is not the initial reaction to a stressor.
The alarm reaction is the first phase of the general adaptation syndrome. It is the immediate response to a stressor, where the body recognizes the stress and initiates a "fight or flight" response. In this scenario, Mike has just received the news of being fired, which is a sudden and unexpected stressor. Therefore, he is most likely experiencing the alarm reaction phase.
Adjustment is not a recognized phase in the general adaptation syndrome. The GAS model consists of three stages: alarm reaction, resistance, and exhaustion. Therefore, this option is not applicable in this context.
The exhaustion phase is the third and final stage of the general adaptation syndrome. It occurs when the body's resources are depleted after prolonged exposure to a stressor, leading to decreased stress resistance and potential health issues. Since Mike has just learned about his job loss, he is unlikely to be in this phase immediately.