The right answer is Calcium.
Calcium (Ca) is one of three secondary nutrients required by plants for healthy growth - the other two nutrients being magnesium (Mg) and sulfur (S).
Role of calcium
Calcium, in the form of calcium pectinate, is responsible for the cohesion of the cell walls of plants. When there is calcium deficiency, new tissues, such as root tips, young leaves and shoot tips, are often deformed due to poor cell wall formation. Calcium is also used as an enzymatic cofactor and for the transmission of signals that coordinate certain cellular activities.
