Question 3
Arrange the salts deposited in a saltern in order of decreasing solubility.
The right answer is the one marked above.
MgCl2, NaCl, CaSO4, CaCO3. A salt crystallises once its saturation point is passed, so the least soluble comes out first. The order of deposition is therefore the order of increasing solubility, and reversing it gives the answer.
Starting with calcium carbonate is the order they are deposited in — that is increasing solubility, which is the question read backwards.