The boiling point of water is a scalding-hot 100 degrees Celsius at sea level. Adding impurities to it, such as common kitchen salt, lowers its vapor pressure and raises the energy requirement needed to make it boil.
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Adding common kitchen salt, or NaCl, to water causes it to dissolve into nitrogen and chloride ions, absorbing energy from the water itself. This also means that it takes more energy for the overall solution to vaporize, or reach the boiling point, so that the salt water solution is at a higher temperature than it would otherwise have been when it vaporizes.
Adding salt to water is generally useful when cooking. The greater boiling temperature means that foods such as noodles and root vegetables like potatoes cook faster and more thoroughly.