Correct Option (c):
Sodium is not considered an essential micronutrient for the majority of plant species. While it can be beneficial for certain plants, particularly C4 and CAM plants like sugar beet and barley, it is not universally required for all plants to complete their life cycle or for fundamental metabolic processes. Essential micronutrients, by definition, are indispensable for plant growth and reproduction, and their absence leads to specific deficiency symptoms.
Incorrect Options:
Boron:
Boron is an essential micronutrient vital for cell wall formation, sugar transport, and reproductive growth, including pollen germination and tube growth.
Zinc:
Zinc is an essential micronutrient that plays a crucial role as a cofactor for various enzymes and is involved in the synthesis of auxins (plant hormones) and protein metabolism.
Copper:
Copper is an essential micronutrient required for photosynthesis (as a component of plastocyanin), respiration, and lignin synthesis, contributing to structural integrity.