Which one of the following is 'Arnon's criterion for essentiality' of element?

Options

A. in the abdsence of element plant do not complete their life cycle or set seeds
B. Deficiency of element cannot be met by supplying other element
C. Element must be directly involved in metabolism of the plant
D. all of the above

Answer

To answer the question regarding "Arnon's criterion for essentiality" of an element, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Essential Nutrients**:
- Essential nutrients for plants are classified into two categories: macronutrients (needed in larger amounts) and micronutrients (needed in smaller amounts).

2. **Criteria for Essentiality**:
- According to Arnon's criterion, for an element to be considered essential, it must fulfill certain conditions:
a. The element must be absolutely necessary for supporting normal growth and reproduction.
b. The absence of the element must prevent the plant from completing its life cycle or setting seeds.
c. The element must be specific and irreplaceable; it cannot be substituted with other elements.
d. The element must be directly involved in the metabolism of the plant.

3. **Evaluating the Options**:
- Based on the criteria mentioned above, we assess the provided options to determine which one correctly represents Arnon's criterion for essentiality.

4. **Conclusion**:
- Since all the mentioned criteria are valid and necessary for an element to be deemed essential, the correct answer is that all of the criteria are applicable. Therefore, the answer is option 4: "All of the above."