what is the difference between isomorphism and polymorphism pls explain with some examples too..

Isomorphism- Iso means equal and morphe means shape. The crystals which have same compositions but different crystalline form. Example, Calcite and Aragonite, these are two different minerals. They both are calcium carbonate minerals but they have different crystalline structures.
Polymorphism - Poly means many. The elements or substance which exist in more than one form are said to exhibit polymorphism. For example, carbon exists as diamond, graphite, fullerene etc.