For synthesis of IAA in plants, . . . . . . . . mineral is essential.

Answer: Option A

For the synthesis of IAA in plants, Zinc is essential.
IAA is indole acetic acid (Auxin) that can be synthesized through the precursor tryptophan known as the TRP-dependent IAA biosynthetic pathway.
Zinc is an essential plant micronutrient and soil availability is of great importance in many crops. Many enzymes include zinc as a cofactor, like acholol dehydrogenase, and carbonic anhydrase. And deficiency of zinc deficiency inhibits protein synthesis.
Plants require zinc for the synthesis of tryptophan, a key amino acid in the synthesis of auxin indole acetic acid. Its control of plant development through action on auxins.