Final answer:
The taste modality with the fewest receptors on the tongue is bitter, which is associated with detecting potentially toxic substances, while the submodality sensitive to the pH of saliva is sour.
Step-by-step explanation:
Of the basic taste modalities which include sweet, sour, bitter, salty, and umami, the one with the fewest taste receptors is bitter. Taste receptors are located on the tongue and are grouped into structures called taste buds. We have different types of taste buds, such as fungiform and circumvallate papillae, which are sensitive to different tastes. The sense of taste, also known as gustation, has historically recognized four main tastes, but more recently, the taste for umami, which is associated with savory foods rich in protein, was identified. There is even some evidence for a sixth taste that detects lipids or fats. The submodality that is sensitive to the pH of saliva is the sour taste, which is attributable to foods with high acidity.