Here's why:

* Peptone is a mixture: It's not a single, pure compound. Instead, it's a complex mixture of peptides and amino acids.

* Variable composition: The exact composition of peptone varies depending on the source material (like casein, gelatin, or meat) and the method of production.

Therefore, you can't assign a single molecular formula to peptone. It's more accurately described as a complex mixture of varying peptides and amino acids.