Question

A coin sink when placed on the surface of water give teasons

Answer 1

It is all about the amount of water they displace. If the weight of the water displaced is heavier than the object it will float, otherwise it will sink. 

A coin is solid and displaces an amount of water that weighs less than the coin so it sinks. 

A ship is hollow so the weight of the water it displaces is more than the ship.