Question

Why does the volume of a solution remains unchanged even after adding the solute to it

Answer 1

the volume remains the same

Answer 2

An aqueous solution consist of atleast two components, the solvent and the solute. Its important that the molarity is defined as moles of salute per liter of solution, not moles of solute per liter of solvent. This is because when we add a substance, perhaps a salt, to some volume of water, the resulting solution will be different than the original volumn in some unpredictable way.