The right answer is water.
A condensation reaction can sometimes release as a product a molecule of water. We sometimes speak of synthesis by dehydration. This is, for example, the case for two monosaccharides, such as glucose or fructose, which can condense into a disaccharide (sucrose) via dehydration synthesis. The reverse reaction is then hydrolysis, the water recombining with the two hydroxyl groups, the disaccharide being converted back into two monosaccharides.
