The inorganic substance always produced as a byproduct of dehydration synthesis is water (H₂O).

Here's why:

* Dehydration synthesis is a chemical reaction that builds larger molecules from smaller ones by removing a water molecule.

* The process involves the joining of two monomers (building blocks) where a hydroxyl group (-OH) from one monomer and a hydrogen atom (-H) from the other are removed, forming a water molecule.

Therefore, water is always a product of dehydration synthesis, regardless of the specific monomers involved.