There is a narrow range of concentration at which the elements are optimum. This statement is concerned with :-

Options

A. Tracer elements
B. Small sized elements
C. Micronutrients
D. Balancing elements

Answer

To solve the question "There is a narrow range of concentration at which the elements are optimum. This statement is concerned with:", we can break it down into the following steps:

### Step-by-Step Solution:

1. **Understanding Nutrient Requirements**:
- Plants and animals require various nutrients for growth and development. These nutrients can be categorized into macronutrients and micronutrients based on the quantity needed.

2. **Defining Macronutrients and Micronutrients**:
- Macronutrients are required in larger quantities (e.g., carbohydrates, fats, proteins).
- Micronutrients are required in smaller quantities (e.g., sulfur, magnesium, phosphate).

3. **Critical Concentration**:
- The statement refers to a "narrow range of concentration," which indicates that there is an optimal level of these nutrients that must be maintained for proper growth.
- This optimal level is often referred to as "critical concentration."

4. **Implications of Concentration Levels**:
- If the concentration of these nutrients falls below or exceeds this critical range, it can lead to deficiencies or toxicities, adversely affecting plant and animal health.

5. **Conclusion**:
- Therefore, the statement is concerned with the concept of "critical concentration" of nutrients, which is essential for the optimal growth and development of plants and animals.

### Final Answer:
The statement is concerned with the concept of "critical concentration" of nutrients in plants and animals.

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