Explanation

Both (a) and (b). Essential elements can be grouped into four broad categories on the basis of their diverse functions (i) Essential elements that acts as a components of biomolecules and hence, structural elements of cells ($e.g.,$ carbon, hydrogen, oxygen and nitrogen) (ii) Essential elements that are components of energy-related chemical compounds in plants (iii) Essential elements that activates or inhibits enzymes (iv) Some essential elements can alter the osmotic potential of a cell