CREATE TABLE table_204_56 (id DECIMAL, "year" DECIMAL, "song" TEXT, "us r&b" DECIMAL, "us rap" DECIMAL, "album" TEXT)

what song made it to the highest rank on the us rap charts ?
SELECT "song" FROM table_204_56 ORDER BY "us rap" LIMIT 1
SELECT "song" FROM "table_204_56" ORDER BY "us rap" NULLS FIRST LIMIT 1