Final answer:
The client's behavior of checking the lock on his apartment door 25 times is an attempt to reduce anxiety related to obsessive-compulsive disorder (OCD).
Step-by-step explanation:
The client's behavior of checking the lock on his apartment door 25 times before leaving for an appointment represents his attempt to reduce anxiety. Obsessive-compulsive disorder (OCD) is characterized by repetitive behaviors and an intense need to perform certain rituals to alleviate anxiety. In this case, the client believes that checking the lock numerous times will ensure the safety of his home and reduce his anxiety.