Which of the following is a synonym for acarpous?

The term "acarpous" refers to something that is incapable of producing fruit or seeds, essentially meaning barren or unfruitful. In this context, the synonym that aligns most closely with this definition is "barren." This word captures the essence of being empty or devoid of productive capacity, making it the correct choice.

The other options present concepts associated with productivity or abundance. "Fecund" and "fertile" both imply a high capacity for growth and reproduction, which contrasts with the notion of being acarpous. Similarly, "rich" may suggest wealth or abundance, but does not share the same connotation of being fruitless or unable to bear. Therefore, the best synonym for acarpous is indeed "barren," as it directly reflects the lack of productive output.