Question

explain why sodium chloride solution is regarded as a mixture while sodium chloride itself is a pure substance

Answer 1

Sodium Chloride is an ionic compound and will contain ions of sodium chloride only therefore it is a pure substance. However sodium chloride solution is prepared by mixing sodium chloride in water. In the solution the sodium chloride simply dissolves in water, it does not react with water to form a new substance and sodium chloride can be separated from water by simple evaporation, thus it is a mixture and contains two components water and sodium chloride.