Which one of the following substances is usually used in cold countries to melt ice accumulated on the roads during winter?

How Salt Melts IceThe process is based on a scientific principle called freezing-point depression:Lowering the Freezing Point: Pure water freezes at 0°C (32°F). When salt is added, it dissolves into the thin film of liquid water on the surface of the ice, creating a brine (saltwater) solution.The Brine Effect: This brine has a much lower freezing point than pure water. Depending on the concentration, it can prevent water from refreezing at temperatures as low as -9°C (15°F).Disrupting the Structure: The salt ions ($Na^+$ and $Cl^-$) get in the way of water molecules trying to bind together into a solid ice crystal structure.Why the other options aren't typically used for roads:Urea: While it is sometimes used as a "pet-friendly" or "airport-safe" de-icer because it is less corrosive than salt, it is much more expensive and can cause nutrient runoff (leading to algae blooms) in local waterways.Boric Acid: This is primarily used as an insecticide or antiseptic; it does not have the necessary properties for large-scale de-icing.Hydrogen Peroxide: This is an oxidizing agent and bleach; it would be ineffective and potentially hazardous if poured onto roads in bulk.Pro Tip: Once the temperature drops below -10°C (14°F), standard rock salt loses its effectiveness. In these extreme conditions, road crews often switch to Calcium Chloride or Magnesium Chloride, which can melt ice at much lower temperatures.