What volume of 16 M nitric acid must be diluted with distilled water to prepare 500.0 mL of 0.50 M HNO3?

Answer 1

500 ml of the diluted 0.50 M nitric acid will contain 0.25 moles of HNO3.
1/64 liter of 16M nitric acid contains 16/64 = 0.25 moles of HNO3. So 1/64 liter (62.5 mL) is the answer.