Which of the following trace elements is essential for auxin synthesis in plants?

In parthenocarpic fruits,the enlargement of the ovary into a fruit is brought about by the auxin . . . . . . .

In plants,auxin synthesis occurs in

The most common auxin is

Auxins are growth hormones capable of promoting cell elongation. They have been used in horticulture to promote growth,flowering,and rooting. Write a line to explain the meaning of the following terms related to auxins:
$(a)$ Auxin precursors
$(b)$ Antiauxins
$(c)$ Synthetic auxins

The primary precursor of $IAA$ is