Final answer:
Adding a common ion can decrease the concentration of the dissolved ion in a saturated solution, increasing the amount of undissolved compound. Complex ions can also increase the solubility of ionic compounds. Adding more solid compound will increase the amount of undissolved compound in a saturated solution. The correct answers are option: b. Add NaOH(aq) and d. Add Zn(OH)₂(S).
Step-by-step explanation:
(b) Adding a common ion, OH¯, will increase the concentration of this ion and shift the solubility equilibrium to the left, decreasing the concentration of magnesium ion and increasing the amount of undissolved magnesium hydroxide.
The solubility of ionic compounds may also be increased when dissolution is coupled to the formation of a complex ion. For example, aluminum hydroxide dissolves in a solution of sodium hydroxide or another strong base because of the formation of the complex ion Al(OH)4.
(d) Adding more solid magnesium hydroxide will increase the amount of undissolved compound in the mixture. The solution is already saturated, though, so the concentrations of dissolved magnesium and hydroxide ions will remain the same.