Final answer:
Opera Seria is the prevalent form of classical opera focused on the noble and heroic themes of Greek legends and affairs of nobility, characterized by an intense emotional narrative.
Step-by-step explanation:
During the Classical era, the prevalent form of opera that concerned itself mainly with the affairs of nobility and Greek legends was Opera Seria. This genre of opera dominated European stages for a significant part of the 18th century. It was heavily influenced by classical Greek drama and focused on intense emotional narratives with a strong emphasis on heroic and noble characters, often dealing with themes such as honor, love, and betrayal. These operas were characterized by their serious tone, elaborate arias, and use of mythological or historical subjects.