Correct answer is D because pinus is the one which is gymnosperm which means that they produce naked seeds or produce seeds but do not produce fruit.

Introduction:
This question belongs to the NEET category and requires us to identify a plant that forms seeds but no fruit. In order to provide a detailed answer, we will examine each option and explain why it does or does not fit the criteria.

A. Ginkgo:
Ginkgo is a gymnosperm, which means it produces naked seeds that are not enclosed within a fruit. Therefore, it does form seeds but no fruit, making it a potential answer to the question.

B. Potato:
Potato is a tuberous crop that belongs to the Solanaceae family. While it does produce seeds, it also forms fruits known as berries. Therefore, it does not meet the criteria of the question.

C. Mustard:
Mustard is an annual plant from the Brassicaceae family. It produces seeds that are used as a spice or for oil extraction. However, mustard plants also form fruits known as siliques or seed pods. Thus, it does not fit the criteria of the question.

D. Pinus:
Pinus, commonly known as pine trees, are gymnosperms that produce seeds. These seeds are not enclosed within a fruit, but rather protected by cones. The cones of pine trees serve as the reproductive structure and contain the seeds. Therefore, pinus plants do form seeds but no fruits, making them a potential answer to the question.

Conclusion:
After examining each option, we can conclude that the plant that forms seeds but no fruit is A. Ginkgo and D. Pinus. Both of these plants are gymnosperms that produce seeds, but do not form fruits.