CBSE Class 9 Answered

When an ice cube (or an iceberg, which is a big ice cube) floats in water, then by definition the weight of the liquid dispaced by the ice cube is  equal to the buoyant force. ( Archimedes Principle).

When the ice cube melts, its volume changes, but its weight is conserved (law of the conservation of mass). So the melted water from the ice cube has exactly the same weight as the water that was displaced by the ice cube when it was frozen.

Density of water is 1g/cc while density of ice is 0.9g/cc.

Let us use some numbers to understand this-

If 9g of water with volume 9cc freezes, it forms 10cc of ice.

When 9g of ice (volume of ice is 10cc) is submerged in water it will displace 9cc of water. So the rise in level is 9cc.

But when 9g of ice melts it  forms water with a volume of 9cc.

So there is no change in level when ice melts.