Question

explain Archimedes principle explain the reason that cork float in water where iron nail sink

Answer 1

It's happen due to the variation of density.  A cork floats in the water whereas an iron nail sinks because the density of cork is less than the density of water. This means that the upthrust of water on the cork is greater than the weight of the cork.

Hope it helps

Answer 2

Archimedes' principle states that the upward buoyant force that is exerted on a body immersed in a fluid, whether fully or partially submerged, is equal to the weight of the fluid that the body displaces and acts in the upward direction at the center of mass of the displaced fluid