Final answer:
The sour taste of grapefruit is attributed to citric acid, a carboxylic acid found in many citrus fruits responsible for their tart flavor.
Step-by-step explanation:
The sour taste of grapefruit is due to citric acid. Carboxylic acids, which have one or more ionizable protons in their hydroxyl (-OH) groups, are responsible for the sour taste in many fruits.
Citric acid, a large carboxylic acid with three ionizable hydrogen atoms, is particularly known for giving citrus fruits such as oranges, lemons, and grapefruits their characteristically sour or tart flavor.
On the other hand, other compounds like acetic acid, ammonia, and sodium chloride are associated with different tastes or properties.
Acetic acid is known for the sour taste of vinegar, ammonia is a weak base with a pungent smell and taste, and sodium chloride is common table salt, which tastes salty, not sour.