Among all the residential areas in Arecibo county, what is the zip_code of the one with the highest white population?
"ARECIBO" is the county; highest white population refers to Max(white_population)
SELECT T1.zip_code FROM zip_data AS T1 INNER JOIN country AS T2 ON T1.zip_code = T2.zip_code WHERE T2.county = 'ARECIBO' ORDER BY T1.white_population DESC LIMIT 1