What is melting point depression? and when it accurse?

A melting point is the characteristic physical property of a substance. So melting point analysis is one of the simplest and most useful techniques for identifing of a chemical substance. Melting point analysis can also provide information about the purity of a sample. A substance containing soluble impurities usually melts at a lower temperature than the pure compound. It can also melt over a wide range of temperatures. The smaller the range of melting temperatures, the higher the purity of the sample.