Question

an ironnail sinks in water but ship made of iron float

Answer 1

because the area of iron nail is less so pressure is more and area of ship is less as compared to its whole size
conclusion. pressure is directly proportional to the area

Answer 2

this depends on the buoyancy of the object.
buoyancy is nothing but the upward force exerted by any fluid.
buoyancy depends upon volume, density, and g that is gravitational acceleration
buoyancy is directly proportional to the volume
more the volume more the buoyancy, less the volume less will be the buoyancy
as the volume of the iron nail is less upthrust acts less hence it sinks in water.
as the volume(space) occupied by ship is more upthrust is more hence it floats
, therefore, iron nail sinks in water but ship made of iron flots