The correct option is
D Cadmium
Plants require 17 essential minerals for optimum growth. According to the quantity required these essential minerals can be grouped into two classes- 9 macronutrients (carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium, sulphur, calcium, magnesium) required in large quantity and 8 micronutrients (iron, molybdenum, boron, chlorine, zinc, nickel, copper, manganese) required in smaller quantity.
Other than these 17 essential minerals plants also absorb a number of non essential minerals. These minerals are absorbed non specifically, because they happen to be present in soil solution and are swept with the water current to inside the plant.
Cadmium is a non essential mineral not required by plants but may be present in plant ash. In fact cadmium is a heavy metal pollutant and is harmful to plants.