Which is not a trace element ?

Options

A. Mn
B. Cu
C. Mo
D. K

Answer

To determine which element is not a trace element, we need to understand the classification of essential elements in plants.

### Step-by-Step Solution:

1. **Understand Essential Elements**: Essential elements are required by plants for growth and development. They are categorized into two main types: macronutrients and micronutrients (or trace elements).

2. **Identify Macronutrients**: Macronutrients are elements that plants need in larger quantities. Key macronutrients include:
- Carbon (C)
- Hydrogen (H)
- Oxygen (O)
- Nitrogen (N)
- Phosphorus (P)
- Sulfur (S)
- Potassium (K)
- Magnesium (Mg)
- Calcium (Ca)

3. **Identify Micronutrients (Trace Elements)**: Micronutrients, or trace elements, are required in very small amounts. Examples include:
- Iron (Fe)
- Chlorine (Cl)
- Manganese (Mn)
- Boron (B)
- Copper (Cu)
- Molybdenum (Mo)
- Zinc (Zn)

4. **Analyze the Given Options**: The question provides the following options:
- Manganese (Mn)
- Copper (Cu)
- Molybdenum (Mo)
- Potassium (K)

5. **Classify Each Option**:
- **Manganese**: Trace element (micronutrient)
- **Copper**: Trace element (micronutrient)
- **Molybdenum**: Trace element (micronutrient)
- **Potassium**: Macronutrient

6. **Conclusion**: Since potassium is classified as a macronutrient and not a trace element, the correct answer to the question "Which is not a trace element?" is **Potassium (K)**.

### Final Answer:
**Potassium (K)** is not a trace element.

---