A pure substance consists of only one kind of matter, that is,
all the particles are same. It has a definite composition and constant
properties. It cannot be split into simpler substances by physical
means. All pure substances have characteristic melting and boiling
points. A pure substance is either a compound or an element.
A Mixture contains two or more substances in any proportion which can be separated by physical methods. Mixtures are generally of two types: Homogeneous
and Heterogeneous. In a mixture, the constituents can be present in any
ratio. They do not have characteristic melting and boiling points. In a
mixture each constituent retain its original properties. These can be
separated by physical means.