Question 2
Which salt is deposited first, in the large shallow ponds of a saltern?
The right answer is the one marked above.
Calcium carbonate. It comes out when the concentration has risen to about twice that of the original sea water — the earliest of the four, because it is the least soluble.
The order the salts come out in is simply the order of their solubilities, least soluble first. Sodium chloride needs about ten times the original concentration, and the two magnesium salts come out after that.