The correct option is D All of the above
Nutrients can be divided into macronutrients and micronutrients based on their requirement inside a plant.
Macronutrients are required in amounts greater than 10 mmol per kg of dry matter. They include C, H, O, P, K, N, S, Mg, Ca.
Micronutrients are required in quantities less than 10 mmol per kg of dry matter. They include Fe, Mn, Cu, Mo, Zn, B, Cl, Ni.
There are certain other elements as well known as beneficial elements- Na, Si, Co, Se. These are required by higher plants.
Critical concentration is the concentration of essential elements below which plant growth is retarded. Below critical concentration, plants develop deficiency symptoms and above critical concentration, they exhibit toxicity symptoms.
Deficiency of Mg leads to premature falling off of leaves and buds in young plants and formation of anthocyanin in older leaves.
Deficiency of Cu leads to premature falling off of leaves and buds in young plants, die back of citrus and reclamation disease of cereals.
Deficiency of P leads to premature falling off of leaves and buds in young plants, poor vascular tissues and inhibition of seed germination.