Which of the following is not essential for all plants ?

Options

A. Mg
B. Co
C. Mo
D. Ni

Answer

To determine which of the following elements is not essential for all plants—magnesium, cobalt, molybdenum, or nickel—we can follow these steps:

### Step-by-Step Solution:

1. **Understand Essential Nutrients**:
- Plants require certain nutrients for growth and development, which are categorized into macronutrients and micronutrients.

2. **Identify Macronutrients**:
- Macronutrients are needed in larger quantities and include nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur.

3. **Identify Micronutrients**:
- Micronutrients are required in smaller amounts and include elements like boron, chlorine, copper, iron, manganese, molybdenum, nickel, and zinc.

4. **Evaluate the Options**:
- The options provided are magnesium, cobalt, molybdenum, and nickel.
- Magnesium is a macronutrient essential for all plants.
- Molybdenum and nickel are both considered micronutrients that are essential for certain plant functions.

5. **Identify the Non-Essential Element**:
- Cobalt is not listed among the essential nutrients for all plants. While some plants may require it in trace amounts, it is not universally essential like the other listed elements.

6. **Conclusion**:
- Therefore, the element that is not essential for all plants is **cobalt**.

### Final Answer:
Cobalt is not essential for all plants.

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