Question

We can't rejoin the broken peice of chalk easily give reason!!?

Answer 1

The chalks are made up of calcium carbonate. When it is broken, it breaks the chemical change and chemical change cannot be reversed.

So, it does not rejoin anymore. The chalk is broken so it is made up of calcium carbonate and chemical changes may be changed. It does not rejoin.

Answer 2

This is because of adhesive and cohesive forces.

The cohesive forces are stronger than adhesive force.

Adhesive force is the force between molecules of same type, here referred to the same type of molecules in chalk.

Cohesive force is the force between molecules of different types.