Option 1, Maize is not transplanted. It is typically directly sowed in the field where it will grow and be harvested.

Option 2, Sorghum also doesn`t require transplanting. Like maize, the seeds are directly sowed in the field.

Option 3, Onion is the correct answer. Onion seedlings are usually started indoors or in a greenhouse and then transplanted to their final growing location. This allows for optimal growing conditions during the early stages of their development which ensures a healthier and more productive crop.

Option 4, Soybean plants are not transplanted; they are directly sowed into the ground just like maize and sorghum. The seeds germinate in the soil where they will eventually grow into mature plants. Thus, they do not involve a transplanting process.

In conclusion, among these four options, only onions are cultivated by transplanting seedlings.