The answer is A, because of the chemical reaction taking place color can change (as in this case). Hope it helps!
Magnet to remove the iron, filter paper (or some filter that could trap sand) to remove the sand, and heat up the salt and water, causing the water to evaporate to separate them.
Answer: 4.4 x 10^-7
Explanation:
The dissociation equation for this reaction is:
MgCO3 (s) → Mg+2 (aq) + CO3-2 (aq)
(Here 0.08 >>> x )

So the solubility MgCO₃ in a solution that containing 0.080 M Mg²⁺ is 4.4 x 10^-7