If 1 mole of each of the following substances were dissolved in 1 liter of water, which solution would contain the highest concentration of OH- ions?

• A. H2SO4
• B. NH4Cl
• C. NaOH
• D. KNO3

Answer: (C)

The main idea is how much hydroxide ions come from a substance that directly provides them versus how acids or neutral salts affect the water equilibrium. A strong base like NaOH completely dissociates in water, giving 1 mole of OH- per mole of NaOH. Dissolving 1 mole in 1 liter yields [OH-] = 1 M, which is far higher than any other option.

In contrast, a strong acid such as H2SO4 pumps lots of H+ into the solution, shifting the water equilibrium toward more H3O+ and suppressing OH-. Ammonium chloride adds NH4+, which is acidic in water, also lowering OH- concentration. A salt like KNO3 from a strong acid and strong base is essentially neutral, leaving the OH- level close to the water autoionization value (~10^-7 M). So, the solution from the strong base dominates with the highest hydroxide concentration.