The normal limit of blood sugar in a fasting person is option 3, which is 70-100 mg/dL. This means that a normal person`s blood sugar level should be between 70 and 100 milligrams per deciliter (mg/dL) after an overnight fast. Blood sugar levels outside of this range may indicate a medical condition such as diabetes mellitus. Option 1, which is 40-60 mg/dL, is incorrect as these levels are too low and could suggest hypoglycemia. Option 2, which is 120-150 mg/dL, and option 4, which is 160-200 mg/dL, are both incorrect as these levels are higher than the normal range for fasting blood sugar. It`s important to regularly monitor blood sugar levels and consult with a healthcare professional if abnormalities are noted.