Question 1
Activities 3.1.6 and 3.1.7 are repeated using water at about 80 °C instead of room-temperature water. What happens to the mass of solute that dissolves?
The right answer is the one marked above.
More dissolves. Raising the temperature increases the solubility of most solutes in a solvent.
This is exactly why the definition of solubility insists on a stated temperature. Quoting 53.0 g for magnesium chloride without saying 25 °C is not a precise statement.