The correct answer is less than 0.5 gram of fat per serving.
According to the Food and Drug Administration, the % of fat-free must comprise 3 grams or less than of the overall fat for a given reference amount. A 100 percent fat-free claim may be made only on foods, which meet the criteria for fat-free and also comprise less than 0.5 grams of fat per 100 grams and comprise no supplementary fat.