Which of the following is not an essential element but is required by the higher plants?

Options

A. Nickel
B. Boron
C. Chlorine
D. Cobalt

Answer

To solve the question "Which of the following is not an essential element but is required by the higher plants?", we can follow these steps:

### Step 1: Understand the Definitions
- **Essential Elements**: These are elements that are necessary for the growth and development of plants. They play a crucial role in various physiological processes.
- **Non-Essential Elements**: These are elements that are not critical for plant growth but may still be required in very small quantities for certain metabolic activities.

### Step 2: Identify the Elements
- We need to look at the options provided in the question. The elements mentioned in the video transcript as examples of non-essential elements include sodium, aluminum, and cobalt.

### Step 3: Analyze the Options
- The options given are:
1. Nickel
2. Boron
3. Chlorine
4. Cobalt

### Step 4: Classify Each Element
- **Nickel**: Essential for certain enzyme functions.
- **Boron**: Essential for cell wall formation and reproductive development.
- **Chlorine**: Essential for photosynthesis and osmosis.
- **Cobalt**: Not essential for plant growth but required in minute quantities for certain metabolic processes.

### Step 5: Conclusion
- Based on the classifications, **Cobalt** is the only element listed that is not essential for the growth of higher plants but is still required in small amounts for metabolic activities. Therefore, the correct answer is **Cobalt**.

### Final Answer
Cobalt is not an essential element but is required by higher plants.

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