Final answer:
The Activity Theory challenges the notion that older adults are in despair because of social isolation by emphasizing the importance of maintaining activities and social involvement.
Step-by-step explanation:
The theory that challenges the notion that older adults are in despair because of social isolation is the Activity Theory. According to this theory, the more active and involved an elderly person is, the happier he or she will be. It suggests that maintaining activities and finding replacements for lost roles are key to enjoying old age and feeling satisfied.