Which of the following is an example of a mood disorder?

Major depressive disorder is classified as a mood disorder due to its defining characteristics, which mainly revolve around significant disturbances in emotional regulation. This disorder involves persistent feelings of sadness, hopelessness, and a lack of interest or pleasure in previously enjoyed activities. These emotional symptoms can affect a person's ability to function in daily life and may also include physical symptoms such as changes in appetite or sleep patterns.

Mood disorders primarily involve the experience of elevated or diminished moods that affect a person's overall emotional and psychological state. Major depressive disorder specifically manifests through these mood alterations and can significantly impact a person's quality of life.

In contrast, the other options relate to different categories of mental health conditions. Generalized anxiety disorder is classified under anxiety disorders and is primarily characterized by excessive worry and anxiety about various aspects of life. Schizophrenia is a severe mental disorder that affects how a person thinks, feels, and behaves, often manifesting through hallucinations and delusions, placing it in the category of psychotic disorders. Obsessive-compulsive disorder involves intrusive thoughts and compulsive behaviors that the individual feels compelled to engage in, categorizing it as an anxiety disorder rather than a mood disorder.