Which word would best describe a 'sharp' or 'keen' sensation, especially in taste or smell?

The term "poignant" is most fitting to describe a 'sharp' or 'keen' sensation, particularly in taste or smell. It conveys an intense and often sharp feeling or experience, frequently associated with strong emotions or perceptual sensations. In the context of taste and smell, something that is poignant would resonate strongly, creating a vivid and almost immediate reaction, such as the rich aroma of spices or the striking flavor of a well-seasoned dish.

In contrast, the other choices do not align as closely with the idea of a sharp sensation. "Infirmity" refers to weakness or illness, which does not relate to sensory experience. "Baleful" carries connotations of something harmful, menacing, or having a threatening quality, which doesn't fit the context of describing taste or smell. "Repast" refers to a meal or the food served at a meal, instead of capturing the quality of sharpness or intensity in sensory experiences.