Why does an iron needle sink in water, but not an iron ship?

What is Cast iron ?

A needle floats in clean water, but sinks in soap solution. Why?

Why does a stone sink when placed on the surface of water?

A cubical box is to be constructed with iron sheets 1 mm in thickness. What can be the minimum value of the external edge so that the cube does not sink in water? Density of iron =8000kg m^-3 and density of water =1000 kgm^-3 .

Write the uses of Pig iron .

Why it is not advisable to slide a magnet on an iron bar back and forth during magnetising it?

Mention the uses of iron.