The correct sentence is: The bike on the bike rack is blue.
All other sentences contain subject-verb agreement errors. Specifically:
- "The surface of the parking lots were redone this summer." should be "The surfaces of the parking lots were redone this summer." or "The surface of the parking lot was redone this summer."
- "The sidewalks in the courtyards has been decorated with chalk." should be "The sidewalks in the courtyards have been decorated with chalk."
- "The cars in the parking lot belongs to the teachers." should be "The cars in the parking lot belong to the teachers."