* Salt (NaCl): Salt lowers the freezing point of water. When you add salt to ice, it dissolves and forms a solution with a lower freezing point than pure water. This means the ice will melt even if the temperature is below the normal freezing point of water (32°F or 0°C).

* Sugar (C12H22O11): Sugar also dissolves in water, but it doesn't have the same effect on the freezing point. It's a non-electrolyte, meaning it doesn't dissociate into ions in solution.

* Chalk (CaCO3): Chalk is mostly calcium carbonate, which is insoluble in water. It won't dissolve and therefore won't affect the freezing point of the water.

In short: Salt is the most effective at melting ice due to its ability to lower the freezing point of water.