Which is not an essential element for plants?

Cadmium is one of the given options that are not an essential element for plants whereas all others like Boron, Iron, and Suplhur are classified as essential elements for plants.
Cadmium has no nutritional value for plants. On the contrary, its presence in soil has various deleterious effects by causing physiological, chemical, and structural changes in plants. Of all the heavy metals, cadmium is considered to be the one that is most toxic for plants.