Final answer:
Clients should monitor their mood to understand the impact of lifestyle changes on mood. The correct option is (1).
Step-by-step explanation:
The main reason why a client with depression, anxiety, or chronic stress should monitor their mood is for the client to understand the impact of their lifestyle changes on mood.
By monitoring their mood, clients can observe how various activities and factors in their life affect their mental state. This information can help them make informed decisions and adjustments to their lifestyle to improve their overall well-being.