Final answer:
A hypomanic episode, without a past major depressive episode or a manic episode, is indicative of Bipolar II disorder. This disorder features periods of hypomania that are less intense than Bipolar I disorder manic episodes and doesn't require a history of major depression for diagnosis. So the correct answer is option (B).
Step-by-step explanation:
A hypomanic episode is sufficient for diagnosis without the presence of a manic episode or a past major depressive episode in the case of b) Bipolar II disorder. Bipolar II disorder is characterized by periods of hypomanic episodes alongside periods of significant depression. However, the hypomanic episodes in Bipolar II disorder are not as severe as the manic episodes that occur in Bipolar I disorder.
It's important to differentiate between the two, as Bipolar I disorder includes at least one full manic episode. On the other hand, cyclothymic disorder may involve hypomanic symptoms and periods of depressive symptoms that are less severe than a major depressive episode without ever fully meeting the criteria for hypomania or major depression.