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.

Deposition is the transition of matter going from gas to solid without passing through the liquid phase.a.) gas—-> solid