Bipolar I disorder is characterized by which of the following?

Bipolar I disorder is primarily characterized by the presence of manic episodes, which may be preceded or followed by hypomanic or major depressive episodes. The defining feature that distinguishes Bipolar I from other forms of mood disorders is the occurrence of at least one manic episode, which is a period of abnormally elevated mood and increased activity or energy lasting at least one week, or requiring hospitalization.

In addition to the manic episodes, individuals with Bipolar I may also experience depressive episodes; however, the presence of mania is the key element for diagnosis. This differentiates it from other disorders such as Bipolar II, where the individual experiences hypomania and depressive episodes, but no full manic episodes.

The other options depict features that are not consistent with Bipolar I disorder. Hypomania, for example, is associated with Bipolar II disorder, where individuals do not experience the full-blown manic episodes required for Bipolar I. Chronic mild depression over an extended period aligns more with Persistent Depressive Disorder (dysthymia) and does not encompass the episodic nature of bipolar disorders.