__ in __ adults experience mental illness.

• A. 1 in 3
• B. 1 in 10
• C. 1 in 50
• D. 1 in 5

Answer: (D)

About one in five adults experience some form of mental illness in a given year. This annual prevalence figure, roughly 20%, is the standard way health researchers express how widespread mental health conditions are in the adult population over a 12-month period. It captures a broad range of conditions—from common issues like anxiety and depression to more severe disorders—so it aligns with the statement asking how many adults are affected in a year. While lifetime prevalence is higher (many people will experience a mental health condition at some point in their lives), the question focuses on a single year, which is why the one-in-five figure is the best match. The other options would understate or overstretch the typical annual reach of mental illness.