At what temperature does salt remain effective as a deicer?

Salt, or sodium chloride, is commonly used as a deicer to lower the freezing point of water, effectively melting ice on roads and walkways. The effectiveness of salt as a deicer diminishes as temperatures drop. While it can start to work at temperatures above 32°F (0°C), its effectiveness starts to significantly decline at lower temperatures.

Salt generally remains effective as a deicer down to about 15°F (-9°C). However, for practical applications, the temperature often cited for optimal effectiveness is around 20°F (-6°C). This is a point where salt can still perform reasonably well without becoming less efficient due to the temperature, making 20°F a common benchmark for its effectiveness.

In this context, the option indicating 22°F stands out as a reasonable estimate for when salt is still usable without being overly affected by cold temperatures. It allows for some margin and acknowledges that while salt is effective at lower temperatures, this specific point (22°F) is when you can expect reduced effectiveness but still reasonable performance compared to much colder temperatures where it might provide little to no benefit.