The answer is b) schedule risk.
Explanation for each option:
a) Resource risk: This type of risk involves the availability or allocation of resources needed for a project. In this scenario, the issue is not about the availability of resources (e.g., ingredients for drinks or a bartender) but rather about timing.
b) Schedule risk: This risk pertains to the timing and scheduling of project activities. In this case, Mike's need to pick up his brother from the airport affects the timing of when he can start making drinks for the gala. This delay impacts the schedule, making it a schedule risk.
c) Assumption risk: This risk arises when assumptions made during project planning turn out to be incorrect. The scenario does not mention any assumptions that have been proven wrong; it is more about a scheduling conflict.
d) Deliverable risk: This risk involves the potential failure to deliver a project output or deliverable. The issue here is not about failing to deliver drinks but rather the timing of when the drinks can be made.
In summary, the primary issue is the timing conflict caused by Mike's need to pick up his brother, which affects the schedule of when he can start making drinks. Therefore, it is a schedule risk.