If each of the salts listed in A through E were dissolved in water to make a 0.1 M solution, which solution would have the lowest pH?

a. NaNO2
b. NaF
c. AlCl3
d. KNO3
e. Na3PO4

The lowest pH means the strongest acid.

I do these this way but your teacher may want another method. I hydrolyze each salt.
NaNO2 + HOH ==> HNO2 + NaOH
HNO2 is a weak acid, NaoH a strong base, the solution will be basic.
NaF + HOH ==> HF + NaOH
HF is a weak acid, NaOH is a strong base, the solution will be basic.
Etc.Find the one that is acidic. In case more than one is acidic, the strongest acid will be the one you want.

To determine which solution would have the lowest pH, we need to consider the nature of the respective anions after the salts dissociate in water.

a. NaNO2: Sodium nitrite (NaNO2) dissociates into Na+ and NO2-. The NO2- ion will not strongly affect the pH of the solution.

b. NaF: Sodium fluoride (NaF) dissociates into Na+ and F-. The F- ion is the conjugate base of the weak acid HF (hydrofluoric acid) and can affect the pH by reacting with water to form HF.

c. AlCl3: Aluminum chloride (AlCl3) dissociates into Al3+ and Cl- ions. The Cl- ion will not strongly affect the pH.

d. KNO3: Potassium nitrate (KNO3) dissociates into K+ and NO3-. The NO3- ion will not strongly affect the pH of the solution.

e. Na3PO4: Sodium phosphate (Na3PO4) dissociates into Na+ and PO43-. The PO43- ion is the conjugate base of phosphoric acid (H3PO4) and can affect the pH by reacting with water to form HPO42-.

Based on the analysis above, the solution with the lowest pH would be the one that contains the conjugate base of a strong acid. In this case, the correct answer is option e. Na3PO4. The PO43- ion can react with water and act as a weak base, resulting in an increase in hydroxide ion (OH-) concentration and a decrease in hydrogen ion (H+) concentration, thus lowering the pH of the solution.