There are five basic taste sensations. select the one mismatched with its stimulating agent. bitter; acids such as those in toxins or poisons umami; amino acids such as glutamate or aspartate found in chicken soup sweet; organic compounds such as sugar sour; hydrogen ions from acids such as those in lemons salty; metal ions such as potassium or sodium

The mismatched pair is bitter; acids such as those in toxins or poisons.   Ligands (stimulating agent) for bitter receptors are molecules like cycloheximide, denatonium, or β-glucopyranosides. Bitterness is the most sensitive of the tastes and it often has unpleasant taste. The most often used bittering agent is caffeine. Bitter foods and beverages include coffee, unsweetened cocoa, olives, citrus peel, beer…

The answer is option a.