Question

what creates the typical smell of marshes? eggs sulphur hydrogen sulfide hydrogen phosphate

Explanation:

In marshes, anaerobic bacteria break down organic matter, producing hydrogen sulfide gas which has a characteristic "rotten - egg" smell. Sulfur alone doesn't create the typical marsh smell. Eggs are not what create the smell of marshes. Hydrogen phosphate is not responsible for the marsh smell.

Answer:

Hydrogen sulfide