Answer:
C Ammonia
Pure water is neutral, so pH is about 7
Vinegar is acidic, pH is around 2-3
Ammonia is alkaline, pH around 11.6
Vitamin C is also acidic, pH is around 3.5 to 6
As pH increases with how alkaline the substance is, substances with a lower pH is more acidic, while substances with a higher pH is more alkaline
the question is asking for the highest pH, so you should choose the most alkaline substance
therefore the ans is C, which is ammonia