Which of the following is not criterion for essentiality of an element?

Options

A. Requirement of the element is specific
B. Necessary for normal growth and reproduction
C. not replaceable by another element
D. indirectly involved in plant metabolism

Explanation

To determine which of the following is not a criterion for the essentiality of an element, we will analyze each option provided.

### Step-by-Step Solution:

1. **Understanding the Criteria for Essentiality**:
- Essential elements for plants must meet certain criteria to be considered necessary for growth and development.

2. **Option Analysis**:
- **Option A: Requirement of the element is specific**: This is a correct criterion. Essential elements must have a specific requirement for the plant.
- **Option B: Necessary for normal growth and reproduction**: This is also a correct criterion. Essential elements are required for normal growth and reproduction in plants.
- **Option C: Not replaceable by another element**: This is another correct criterion. Essential elements cannot be substituted by other elements for their specific functions.
- **Option D: Involved in plant metabolism**: This is the option we need to scrutinize. While many essential elements are involved in plant metabolism, the question asks for a criterion that is not essential for defining an element's essentiality.

3. **Conclusion**:
- The last option, "involved in plant metabolism," is not a strict criterion for the essentiality of an element. While many essential elements participate in metabolic processes, not all essential elements must be directly involved in metabolism to be considered essential.

### Final Answer:
The option that is **not a criterion for the essentiality of an element** is **"involved in plant metabolism."**

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