The correct sentence is: "The Nike on the bike rack is blue."
The other sentences contain subject-verb agreement errors:
- "The cars in the parking lot belong to the teachers."
- "The surface of the parking lot was redone this summer."
- "The sidewalk in the courtyard has been decorated with chalk."
(Note: "courtyards" could be correct if referring to multiple courtyards, but in that case, it should be worded as "The sidewalks in the courtyards...")