The correct answer is: A. Sulphur
Sulphur is an essential element for plant growth and
is absorbed by plants both in cation and anion form. The cation form of sulphur is ammonium (NH4+), while the anion form is sulphate (SO42-). Sulphur is required for the synthesis of proteins, amino acids, and vitamins. It is also involved in the formation of chlorophyll, which is essential for photosynthesis.Nitrogen is also an essential element for plant growth, but it is only absorbed in cation form. The cation form of nitrogen is nitrate (NO3-). Nitrogen is required for the synthesis of proteins, nucleic acids, and chlorophyll.
Calcium is an essential element for plant growth, but it is only absorbed in cation form. The cation form of calcium is calcium (Ca2+). Calcium is required for the formation of cell walls, cell membranes, and the transport of nutrients.
Phosphorus is an essential element for plant growth, but it is only absorbed in anion form. The anion form of phosphorus is phosphate (PO43-). Phosphorus is required for the synthesis of nucleic acids, ATP, and phospholipids.
In conclusion, the element absorbed both in cation and anion form is sulphur.