By the way what do those symbols for the elements have in common (for number 7-11): Pb, Au, Cu, Hg, Na ? *

those have symbols for their Latin or Greek name

Explanation:

hope it helps

Na number of 11

Explanation:

Pb no. 82

Au no. 79

Cu no. 29

Hg no. 80

radioactive decay occurs in unstable atomic nuclei – that is, ones that don't have enough binding energy to hold

the nucleus together due to an excess of either protons or neutrons.

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.