Answer & Explanation
A) 50.0 mL 0.0500 M calcium hydroxide, Ca(OH)2 (aq)
50.0 mL 0.0500 M calcium hydroxide, Ca(OH)2 (aq) has the highest pH value.
Sodium hydroxide and Calcium hydroxide are strong bases so they completely ionize in solution. Because they ionize at the same rate, and Calcium hydroxide has the higher pH calculated, then Calcium hydroxide, in fact, has the highest pH.
Nitric acid is a strong acid, so it completely ionizes in water. Whilst nitrous acid is a weak acid. Therefore, the nitric acid solution has the LOWEST ph.