Answer:A dehydrated brain primarily consists of fats. This is because the brain is rich in lipids, which form a significant part of its structure. While water comprises about 75% of the brain's weight when hydrated, the remaining structure is made up largely of fats. These fats are crucial for constructing cell membranes, insulating nerve fibers (myelin), and supporting overall brain health. Muscle is not a component of the brain, so it would not contribute to the brain's weight in either hydrated or dehydrated states. Hence, in a dehydrated brain, the predominant remaining component by weight is fat.