The correct option is B Boron
Boron is required for uptake and utilisation of Ca, membrane functioning, pollen germination, cell elongation, cell differentiation and carbohydrate translocation.
Magnesium is a constituent of the ring structure of chlorophyll and helps to maintain the ribosome structure.
Chlorine helps in determining the solute concentration and the anion-cation balance in cells.
Potassium helps to maintain an anion-cation balance in cells and is involved in protein synthesis, opening and closing of stomata, activation of enzymes and in maintenance of the turgidity of cells.