What is the correct code for type II bipolar disorder?

Type II bipolar disorder is characterized by episodes of major depression and at least one hypomanic episode, but it does not include episodes of full manic behavior as seen in type I bipolar disorder. The specific code for type II bipolar disorder in the ICD-10 classification system is F31.81, which directly identifies this subtype of mood disorder in a clinical context.

The other codes provided do not correspond to type II bipolar disorder. For instance, F06.31 is for mood disorder due to another medical condition, F03.90 refers to unspecified dementia without behavioral disturbance, and F32.9 is used for a major depressive episode unspecified. These codes serve different diagnostic purposes and do not accurately represent type II bipolar disorder, which is why they are not the appropriate choice in this situation.