Describe a characteristic of a fissionable substance that is essential for a chain-reaction to sustain itself.

The fissionable substance that is essential for a chain reaction in order to sustain itself shows that atomic mass needs to be heavier for it to release more than one neutron. Because of this reaction it is expected to release some energy.

chemical digestion occurs in the stomach were hcl and pepsin forms chyme, the mouth in which salivary amylase breaks down starch to form bolus, and the small intestine specifically the duodenum.

catya your not at all which answer i've seen you do this on another question!