What is a mixture ?

 A mixture is that form of matter in which two or more substances (elements or compounds) are present in any proportion. 

The substances present in a mixture called components or constituents of the mixture. For example, in a mixture of salt and sand, the salt and the sand are the constituents of this mixture. 

The constituents of a mixture can be seperated by simple laboratory methods. The composition of a mixture is not fixed. The constituents of a mixture may be present in any proportion. For example, air is a mixture of mainly oxygen, nitrogen; smaller amounts of carbon dioxide (CO2), dust particles etc, are also present in the air. 

A mixture may be homogeneous or heterogeneous depending upon the nature of the substances present therein.