Solution:
The requirement of the element must be specific and not replaceable by another element.
The element must be directly involved in the metabolism of the plant.
Consider the following w.r.t criteria for essentiality of an element.
(a) In the absence of the element the plants do not complete their life cycle or set the seeds.
(b) Requirements of the element must be specific and replaceable by another element.
(c) Element cannot be directly involved in the metabolism of plant.
(d) Deficiency of any one element cannot be met by supplying some other element.
How many are incorrect?
The requirement of the element must be specific and not replaceable by another element.
The element must be directly involved in the metabolism of the plant.