Classification of essential elements is :

Options

A. A quantitative feature
B. Based on the size of minerals
C. A qualitative feature
D. Based on the size of the plant

Answer

### Step-by-Step Solution:

1. **Understanding Essential Elements**: Essential elements are nutrients that plants require for their growth and development. They are classified based on various criteria.

2. **Classification Based on Quantitative Requirement**: The first basis for classification is the quantitative requirement of these elements by plants. This means how much of each element is needed.

3. **Macro and Micro Elements**:
- **Macro Elements**: These are essential elements required in large amounts. Examples include:
- Carbon (C)
- Hydrogen (H)
- Oxygen (O)
- Nitrogen (N)
- Phosphorus (P)
- Sulfur (S)
- **Micro Elements**: These are required in smaller amounts. Examples include:
- Boron (B)
- Iron (Fe)
- Copper (Cu)
- Molybdenum (Mo)

4. **Classification Based on Function**: The second basis for classification is the function of these elements in the plant. They can be categorized into four types:
- **Structural Elements**: These are components of biomolecules. Examples include:
- Carbon, Hydrogen, Oxygen, and Nitrogen.
- **Energy-Related Compounds**: Elements like Magnesium (Mg) in chlorophyll and Phosphorus (P) in ATP.
- **Enzyme Activators or Inhibitors**: Elements that activate or inhibit enzymes, such as:
- Magnesium (Mg²⁺) for Rubisco and Pepcase enzymes.
- Zinc (Zn²⁺) for Alcohol Dehydrogenase.
- Molybdenum (Mo) as an activator.
- **Maintaining Osmotic Potential**: Elements like Potassium (K) and Chlorine (Cl) help in regulating osmotic potential and stomatal movement.

5. **Conclusion**: Based on the classification discussed, the essential elements are primarily classified based on their quantitative requirement and their function in the plant.

### Final Answer:
The classification of essential elements is based on:
1. Quantitative Requirement (Macro and Micro Elements)
2. Function (Structural, Energy-related, Enzyme Activators/Inhibitors, Osmotic Potential)