What is the name of the opposite chemical process, where a large molecule is split by the addition of water?

The correct answer will be- Hydrolysis reaction

Explanation:

The metabolic reaction which involves the addition of water or the ions of the H₂O molecule which are the -OH and -H ions.  Since these ions will be obtained through the hydrolysis of the water molecule, therefore, the process is known as the hydrolysis reaction.

This reaction is the opposite of the dehydration reaction in which the water molecule is released. The breakdown of the polysaccharides into monosaccharides is a hydrolysis reaction.

Thus, Hydrolysis reaction is the correct answer.