To solve this problem, we need to identify the micronutrient required for the splitting of the water molecule during photosynthesis.$\newline$Let's analyze the role of each micronutrient:$\newline \bullet$Manganese:$\newline$ - Manganese is a crucial component of the oxygen-evolving complex (OEC) in photosystem II.$\newline$ - It plays a vital role in the photolysis of water, which is the process of splitting water molecules to release oxygen, protons, and electrons.$\newline$ - Therefore, manganese is directly involved in the splitting of water during photosynthesis.$\newline \bullet$Molybdenum:$\newline$ - Molybdenum is involved in nitrogen metabolism and is a component of certain enzymes, but it is not directly involved in the splitting of water.$\newline \bullet$Magnesium:$\newline$ - Magnesium is a central atom in the chlorophyll molecule and is essential for capturing light energy, but it does not directly participate in water splitting.$\newline \bullet$Copper:$\newline$ - Copper is involved in electron transport and redox reactions, but it is not directly responsible for the splitting of water.$\newline$Based on this analysis, the correct answer is Option 1: Manganese, as it is essential for the splitting of water molecules during photosynthesis.