Hydroponics or soilless culture helps in knowing

Options

A. essentiality of an element
B. deficiency symptoms caused by an element
C. toxicity caused by an element
D. all of these

Explanation

### Step-by-Step Text Solution:

1. **Understanding Hydroponics**: Hydroponics, also known as soilless culture, refers to a method of growing plants without soil. Instead, plants are cultivated in a nutrient-rich water solution.

2. **Nutrient Solution**: In hydroponics, the water used contains a standard formula of essential nutrients that plants need for growth and development. This allows for precise control over the nutrients available to the plants.

3. **Purpose of Hydroponics**: The primary purpose of hydroponics is to study and understand various aspects of plant nutrition, particularly the essentiality of mineral elements.

4. **Essentiality of Mineral Elements**: Hydroponics helps in determining which mineral elements are essential for plant growth. This means it allows researchers to identify which nutrients are necessary for plants to thrive.

5. **Deficiency Symptoms**: Hydroponics also aids in recognizing deficiency symptoms that occur when a particular nutrient is unavailable or insufficient. By observing plants grown in hydroponic systems, scientists can see how the lack of specific nutrients affects plant health.

6. **Toxicity of Nutrients**: Additionally, hydroponics can help in understanding the toxicity caused by excess amounts of certain nutrients. This means that researchers can study how too much of a nutrient can negatively impact plant health.

7. **Interactions Among Elements**: Hydroponics allows for the investigation of possible interactions among different mineral elements present in plants. This is important for understanding how various nutrients work together in plant metabolism.

8. **Conclusion**: Therefore, hydroponics or soilless culture helps in knowing:
- The essentiality of mineral elements
- Deficiency symptoms caused by the lack of nutrients
- Toxicity caused by excess nutrients
- Interactions among different elements and their roles in plant metabolism.

Thus, the correct answer to the question is that hydroponics helps in knowing all of these aspects.