Final answer:
Marcus's difficulty focusing on work, impulsivity, and excessive talking suggest that he could be diagnosed with adult ADHD, which is a neurodevelopmental disorder affecting attention and impulse control and can continue to impact individuals well into adulthood.
Step-by-step explanation:
Attention Deficit Hyperactivity Disorder:
Marcus is likely to be diagnosed with adult Attention Deficit Hyperactivity Disorder (ADHD). This neurodevelopmental disorder is characterized by significant difficulties in maintaining attention and controlling impulses. Marcus's behaviors, such as being unable to focus on work assignments, a tendency to switch between projects, impulsivity, and incessant talking, are indicative of ADHD symptoms.
The prevalence of ADHD affects approximately three to five percent of adults and children, and symptoms can range from inattention to hyperactivity. In some cases, individuals with ADHD might also have associated issues such as depression or obsessive-compulsive disorder, conditions known as comorbidities. It's important to recognize that ADHD can persist into adulthood, affecting various aspects of life, including job performance and stability.