A PIC cannot exceed how many knots in the airspace underlying class B or in a VFR corridor designated through class B airspace?

The correct answer is based on the regulations that govern airspeed limitations in specific types of airspace. In the airspace beneath Class B airspace or within a VFR corridor designated through Class B airspace, pilots in command (PICs) are restricted to a maximum airspeed of 200 knots. This limitation is in place to help maintain safety and manage the flow of air traffic around busy Class B airspace, which typically involves higher-density operations.

Flying at speeds above this limit could increase the difficulty for air traffic control to manage the various aircraft operations occurring within and around the Class B airspace, potentially leading to unsafe situations. The regulations are designed to ensure that all aircraft operate in a manner that promotes safety and efficiency, especially in areas where commercial air traffic is prevalent.

The other options represent airspeed limits found in different contexts. For instance, 120 and 180 knots may be relevant in certain airspace classifications or under different flight rules, but they do not pertain specifically to the restrictions applied in Class B airspace. Similarly, 250 knots is a limit that applies at lower altitudes outside of specific controlled airspace, highlighting why 200 knots is the correct limit in this scenario.