The correct answer is NH₄Cl.
With the increase in temperature, endothermic reactions are favored. The dissolution of NH₄Cl in water is an example of an endothermic reaction. When the temperature is increased more dissolution of the salt takes place, thus, the solubility of the salt increases.
Hence, it can be said that NH₄Cl will exhibit the greatest change in the solubility per 100 g solvent with an elevation in temperature.