The correct option is B Mg, K
Mobility of elements refers to their transportability within the plant.
Mobile nutrients are nitrogen in the form of nitrate, phosphorus (P) in the form of phosphate, potassium (K), magnesium (Mg), chlorine (Cl), zinc (Zn) and molybdenum (Mo). Calcium (Ca), sulfur (S), iron (Fe), boron (B) and copper (Cu) are immobile.