ANS:B - chlorophyll

Magnesium is present in chlorophyll. Chlorophyll is the green pigment found in the chloroplasts of plants and other photosynthetic organisms. It plays a crucial role in photosynthesis, the process by which plants convert light energy into chemical energy in the form of glucose. Magnesium is a central atom in the chlorophyll molecule, surrounded by a porphyrin ring structure. This magnesium atom is essential for capturing light energy and initiating the photosynthetic process. Therefore, magnesium is intimately involved in the green coloration of plants due to its presence in chlorophyll.