So you happen to have a driveway that is covered with a few inches of ice and you didn't invest in a pick or anything to break it up. No way can you get rid of it with your snow shovel... One of the things that people often employ to help ride themselves of this problem is salt. The reason why it works is that it actually lowers the freezing point of ice so that it will melt, even if it is actually below the normal freezing point outside.
Obviously it is also used heavily on roads and in other public places as it is easily spread and a relatively inexpensive way to slow down accumulation of frozen preciptation or to help what is on the ground melt.
Of course it is important to note that as the temperature starts to dip below 20 degrees fahrenheit, the effectiveness of salt drops very rapidly.
When salt is added to water its freezing point is lowered. This means that the ice will melt at temperature lower than 0 degrees centigrade when salt is added to it. So people add salt to ice so that it will melt faster and its removal by other mechanical means will become easier.
It is important to note that salt sprinkled to on ice acts only on the surface of the ice, But then the melting of the Ice in any case starts from the surface only, and as ice melts with sprinkling of salt, the salt reaches the lower level of ice to melt it further.
when any impurity is added to a substance generally its melting point goes down and so when salt is added to ice it takes heat from the ice to be dissolved and so the melting point goes down and the ice melts