Question

what do you mean by saying that the molality of solution is 0.1

Answer 1

 molality of a solution is defined as the number of moles of solute per kilogram of solvent.

Molality = moles of solute / kilograms of solvent

SI units of molality are: mol/kg

So in your case the molality is 0.1 mol/kg, so 0.1 moles of solute per kilogram of solvent.

Please do not confuse Molality with Molarity. Molarity is something different which takes into consideration the volume of the solution instead of the mass.