Final answer:
Dissociative identity disorder, formerly known as multiple personality disorder, is marked by multiple distinct personality states and various alterations in functioning, causing distress or impairment.
Step-by-step explanation:
The dissociative disorder that was formerly named multiple personality disorder is c) Dissociative identity disorder. This disorder is characterized by the presence of two or more distinct personality states or an experience of possession and involves marked discontinuity in sense of self and sense of agency, accompanied by related alterations in affect, behavior, consciousness, memory, perception, cognition, and/or sensory-motor functioning. These symptoms can cause significant distress or impairment in social, occupational, or other important areas of functioning.