"which water-soluble compound is considered a conditionally essential nutrient for infants"

The water soluble compound that is considered to be conditionally important nutrient for infants would be choline. This substance is supplied to the baby in the womb from the mother. It encourages healthy development before giving birth. It is mostly found in liver, eggs, milk and eggs. When the baby is born, it gets the choline requirement from the breast milk. It is important for the synthesis of a neurotransmitter known as actetylcholine which is important for muscle and nerve function. Also, choline is essential for signaling of the cell membrane, lipid transport, homocysteine reduction and normal functioning of the liver.