Importance of microelements was recognised late due to

Options

A. their toxicity
B. presence as contaminants in macronutrients
C. negligible role played by them in plant physiology
D. leakage from roots.

Answer

### Step-by-Step Solution:

1. **Understanding Mineral Nutrients**:
- There are 17 essential mineral nutrients for plants, which are categorized into macronutrients and micronutrients.
- Macronutrients are required in larger quantities, while micronutrients are needed in smaller amounts.

2. **Definition of Macronutrients and Micronutrients**:
- **Macronutrients**: These are nutrients that plants need in larger quantities. They are easily detectable due to their abundance.
- **Micronutrients**: These are nutrients required in smaller quantities. Their presence is less noticeable, which contributes to their late recognition.

3. **Recognition of Micronutrients**:
- The importance of micronutrients was recognized late primarily because they are present in smaller quantities, making them difficult to detect.
- Additionally, micronutrients were often mistaken for contaminants in the soil due to their low concentrations.

4. **Evaluating the Options**:
- Option 1: **Toxicity** - While some micronutrients can be toxic in high amounts, this is not the primary reason for their late recognition.
- Option 2: **Presence as contaminants in micronutrients** - This option aligns with the idea that they were mistaken for contaminants due to their low levels.
- Option 3: **Negligible role in plant physiology** - This is incorrect as micronutrients do play significant roles in plant health.
- Option 4: **Leakage from roots** - This is not a relevant reason for the late recognition of micronutrients.

5. **Conclusion**:
- The correct answer is **Option 2: Presence as contaminants in micronutrients**. This reflects the misunderstanding of their importance due to their low concentration in the soil.