ANS:D - Carbon

Among the options provided, Carbon does not come under the category of 'micro-nutrient' for plant growth. Explanation:

1. Chlorine: Chlorine is considered a micronutrient for plant growth. It is essential for photosynthesis, osmotic regulation, and various metabolic processes in plants. However, it is required in relatively small quantities compared to macronutrients like nitrogen, phosphorus, and potassium.
2. Iron: Iron is classified as a micronutrient for plants. It plays a crucial role in chlorophyll synthesis, electron transport in photosynthesis, and enzyme activation. Iron deficiency can lead to chlorosis (yellowing of leaves) and reduced plant growth.
3. Boron: Boron is also categorized as a micronutrient. It is involved in cell wall formation, pollen germination, and seed development. Boron deficiency can cause various physiological disorders in plants, such as hollow stems, poor root development, and reduced fruit set.
4. Carbon: Carbon is not typically classified as a nutrient for plants in the context of essential mineral nutrients. While carbon is vital for photosynthesis and forms the backbone of organic molecules in plants, it is primarily obtained from atmospheric carbon dioxide (CO2) through photosynthesis. Plants do not face carbon deficiency under normal conditions, as atmospheric CO2 is readily available for photosynthetic processes.

In summary, carbon is not considered a micronutrient for plant growth, as it is obtained from the atmosphere and is not typically supplied to plants as a fertilizer or nutrient supplement. Instead, it is a fundamental component of organic compounds synthesized by plants during photosynthesis.