Which one of the following elements is relatively immobile in plants?

Elements that are actively mobilized within plants and exported to young developing tissues include nitrogen, potassium, and magnesium. Their deficiency symptoms first appear in older tissues.

Elements that are relatively immobile and are not transported out of mature organs include calcium and sulphur. These elements are structural components of the cell and are not easily released. Their deficiency symptoms first appear in young tissues.

Therefore, sulphur is relatively immobile in plants.

Answer: Sulphur