Final answer:
A score of 90 on the DSM-IV GAF scale is considered optimal functioning.
Step-by-step explanation:
The DSM-IV GAF scale is used to assess the overall level of functioning in individuals with mental disorders. A score of 90 on the GAF scale indicates optimal functioning, which means that the client is functioning well in various areas of life, such as work, relationships, and self-care. This score suggests that the client is experiencing minimal or no impairment due to their mental health condition.