Which one of the following statements can best explain the term critical concentration of an essential element?

Options

A. essential element concentration below which plant growth is retarded
B. essential element concentration below which plant growth becomes enhanced
C. essential element concentration below which plant remains in the vegetative phase
D. None of the above

Explanation

To explain the term "critical concentration of an essential element," we can break down the concept step by step:

### Step-by-Step Solution:

1. **Definition of Critical Concentration**:
- The critical concentration of an essential element refers to the minimum concentration of that element required for normal plant growth and development.

2. **Impact on Plant Growth**:
- When the concentration of an essential element falls below this critical level, it leads to negative effects on plant growth, often referred to as "retarded growth."

3. **Symptoms of Deficiency**:
- As the concentration decreases and reaches the critical level, plants begin to exhibit deficiency symptoms. These symptoms indicate that the plant is not receiving enough of the essential element for optimal functioning.

4. **Identifying the Correct Statement**:
- Among the provided options, the statement that best explains the term critical concentration is: "essential element concentration below which plant growth is retarded." This accurately describes the concept as it highlights the detrimental effects on growth when the concentration is insufficient.

5. **Elimination of Incorrect Options**:
- The other options can be ruled out:
- "Essential element concentration below which plant growth becomes enhanced" is incorrect, as lower concentrations do not enhance growth.
- "Essential elements concentration below which the plant remains in the vegetative phase" is also incorrect, as it does not address the impact on growth.
- "None of the above" is not applicable since we have identified a correct option.

### Final Answer:
The correct statement that best explains the term critical concentration of an essential element is: **"Essential element concentration below which plant growth is retarded."**

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