Huh? Lol I don’t get the question
Bones are made up of Calcium Phosphate given by the chemical formula,
. When bones are kept in Hydrochloric acid, given by the chemical formula, HCl, they become soft because the calcium compound present in the bones changes its form. The following double displacement reaction takes place when the bones are kept in HCl,
---> 
Calcium chloride is water soluble, and gets washed away. This makes the bone thin and soft.
There was no sunlight, in one way or another sunlight is the source of almost all life on the surface of the earth
Insulin is released into the blood when oxygen levels are low and blood glucose levels are high