The parameter pH is a measure of the substance's acidity or basicity. It is quantitatively equal to the negative logarithm of the concentration of H+ ions. So, the lower the pH, the more acidic the substance, Otherwise, the higher the pH the more basic the substance. The pH range runs from 1 to 14, with 7 being neutral.
So, if we are asked to distinguish which of those have the lowest pH, we have to know the moles of H+ ions. Since all of them have a concentration of 0.1 M, concentration is not a factor. Thus, we just have to identify the strongest acid among the list. That is easy to answer because you only have to remember 7 strong acid occurring in nature: HCl, H₂SO₄, HNO₃, HClO₄, HClO₃, HBr, and HI. Since only HNO₃ is included in the list among the choices, the answer would be letter D.
