An essential element is that which

Options

A. (a) is found in plant ash
B. (b) is available in soil
C. (c) improves health of plants
D. (d) is irreplaceable for growth of plants

Answer

**Step-by-Step Text Solution:**

1. **Understanding Essential Elements:** An essential element, also known as an essential nutrient, is a substance that is vital for the growth and reproduction of plants. Without these elements, plants cannot lead a healthy life.

2. **Historical Context:** The concept of essential nutrients was introduced by researchers Hammond and Stout in 1939. They defined essential nutrients based on their necessity for plant growth.

3. **Types of Essential Nutrients:** Essential nutrients are categorized into two types:
- **Macronutrients:** These are required in larger quantities and include elements such as nitrogen, phosphorus, and potassium.
- **Micronutrients:** These are required in smaller quantities but are still crucial for plant health.

4. **Irreplaceability:** Essential nutrients are irreplaceable for the growth and development of plants. This means that without these nutrients, normal growth and reproduction cannot occur.

5. **Evaluating Options:**
- **Option A:** "Is found in plant ash." - This is incorrect as it does not define an essential element.
- **Option B:** "Is available in soil." - This is partially correct, but not comprehensive since some nutrients are obtained from the atmosphere as well.
- **Option C:** "Improves health of plant." - While this is true, it does not fully capture the definition of essential elements.
- **Option D:** "Is irreplaceable for growth of plants." - This is the most accurate and complete definition of an essential element.

6. **Conclusion:** Based on the evaluation of the options, the correct answer is D, as it encapsulates the key characteristic of essential elements in relation to plant growth.