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