If someone can me understand, and figure this problem. if each substance costs the same amount per kilogram (kg), which would be most cost-effective as a way to lower the freezing point of water? (assume complete dissociation for all ionic compounds.) explain. ill post the 5 molecules as a drawing.

The most cost-effective as a way to lower the freezing point of water is SrCl2 because it will form three ions in the solution. The more ions are there in the solution, the more water molecules will be unable to get out of the solution since it is trapped by the ions of the SrCl2. It would not depend on the nature of the substance no matter how heavy or light it is as long as the dissociation of ions in the solution is many then it is enough.

Spontaneity tell us the direction of the reaction, but not how fast it goes. gibbs free energy brings together enthalpy, entropy and temperature in one easy formula. g = h - ts. and, finally the sign of delta g is always negative for a spontaneous reaction.