The reserve food of brown algae is
The reserve food of brown algae is laminarin. The molecule laminarin (also known as laminaran) is a storage glucan (a polysaccharide of glucose) found in brown algae. It is used as a carbohydrate food reserve in the same way, that chrysolaminarin is used by phytoplankton, especially in diatoms. Thus, the correct answer is option C.