Pure water freezes at 32°F (0°C), but saltwater doesn’t play by those rules. When you dissolve salt into water, those tiny particles get in the way of water molecules trying to form ice crystals. The more salt you add, the colder the water needs to get before it solidifies. In fact, typical ocean water, with a salinity of about 3.5%, won’t freeze until the thermometer drops to around 28.4°F (-2°C).
Think of it like a crowded dance floor. Water molecules want to hold hands and form a neat ice pattern, but salt ions are the clumsy dancers bumping into everyone. The music has to get much slower (the temperature much colder) before an orderly arrangement happens. This is why your driveway ice melts when you sprinkle salt—the salt lowers the freezing point, turning solid ice back into slush.
