Adolescents often experience heightened emotions and increased risk-taking behavior. This may be due to delayed development (compared to the limbic system) in which area of the brain?

Prefrontal cortex

Explanation:

The prefrontal cortex is the part of the brain that covers the frontal lobe in the brain. This is the part of the brain that is responsible for decision making, expression of personality, the complexity of cognitive behavior and social behavior. This part of the brain is responsible for concrete learning and another part of the brain is responsible for higher abstract learning.  

Thus here adolescent usually experiences heightened experience of emotions and increase the risk-taking behavior which is the result of the prefrontal cortex.