The flow chart below represents the main steps in the preparation of sodium carbonate​

the element that provides strength to the exoskeletons of clams and oysters is phosphorus. this is so because calcium carbonate is the main component in the shells.

explanation:

as resources become scarce because of population growth, the growth decreases after few years due to lack of resources and food.

there are so many examples for that in different areas, like biology experiment carried out in our lab recently.

here's one link:

the missing space is phylum