Concept:For a healthy green plant, the soil must supply essential mineral nutrients, particularly magnesium for chlorophyll formation.
Explanation:Magnesium ions (
Mg2+) are required by green plants because magnesium is a central atom in the chlorophyll molecule.
This mineral is absorbed from the soil through the roots and is vital for photosynthesis.
Without magnesium, chlorophyll synthesis fails, causing leaves to become pale or yellow instead of healthy green.
Plants make their own amino acids, sugars, and glucose using photosynthesis, so they need a source of carbon dioxide and water rather than soil-provided amino acids, carbon, or glucose salts.
Carbon mainly enters leaves as carbon dioxide gas, not as a soil nutrient for green plants.
Therefore, among the options, magnesium ions are the substance that must be present in the soil for a healthy green plant.
Answer:D. Magnesium ions