While showing some common compounds used in our daily life in the laboratory, the teacher showed sodium chloride compound and told that it is also called common salt. Next day, one of the students brought common salt from home to the laboratory and requested the teacher to show sodium chloride as well. He kept both common salt and sodium chloride in two different watch glasses and left. Next day, during lunch break the student went to the laboratory and saw that the common salt brought from home became sticky whereas the compound sodium chloride remained as it is. What would be the justification given by the teacher for the above observation?

Explanation

In common salt, trace amounts of `MgCl_(2)` and `CaCl_(2)` are present as impurities which are deliquescent in nature. They absorb moisture from the surroundings and are converted into solution. As a result, common salt becomes sticky.