The hydrolysis of a glycosidic bond, which is the bond between two sugar molecules in a glycoside, is typically catalyzed by an acid or an enzyme called a glycosidase. Hydrolysis involves the breaking of the bond with the addition of a water molecule.
In the case of a three-letter answer starting with "H" for your crossword puzzle, "H2O" (water) would be a suitable option. Water is commonly used to catalyze the hydrolysis of glycosidic bonds. It acts as a nucleophile, attacking the glycosidic bond and breaking it, resulting in the formation of separate sugar molecules.
On the other hand, "HCl" (hydrochloric acid) is also capable of catalyzing the hydrolysis of glycosidic bonds. However, it is less commonly used in this context compared to water or specific glycosidase enzymes.
In terms of whether "HCl" can be written down on the crossword, it ultimately depends on the specific rules and guidelines of the crossword puzzle you are solving. Crossword puzzles have their own set of rules and limitations, so it's best to follow the instructions provided by the crossword creator or consult any given clues or hints to ensure the answer fits within the puzzle's constraints.