The stronger the acid the lower the pH, because pH = log { 1 / [H+]}. You can discard easily the options B and C because they are organic acid which are relatively weak. To compare properly the inorganic acids you should use a Ka or pKa table. You can predict that HPO4 (2-) is less strong because the third dissociation is weaker the first. So, you should only need to search for the Ka or pKa of HNO2 and HNO3. Every one who is familiar with the stronger acids knows that HNO3 is one of the strongest acid, stronger indeed than HNO2. So, the strongest acid of the list is HNO3 and it has the lowest pH. Answer: option D. 1.0 M HNO3.
