Hydrochloric Acid (HCl) is produced by the stomach and has the job of breaking down proteins. If you make plenty of HCl, then the body can adequately digest protein. If not, protein digestion is compromised.
The mass number is the sum of the number of protons and number of neutrons the atom has.
So, we can write the equation as:
x + 20 = 40
x = 20 neutrons.
Sedimentary would be your answer. Sediment is the matter that settles to the bottom of a liquid, so as rocks, dirt and mud settled over the dead body it would fossilize inside the sedimentary rock.