Answer:-
Water is highly ordered. In water each oxygen atom is connected to others around it through hydrogen bonding via bridging hydrogen atoms. When a salt like NaCl is dissolved, some of these Hydrogen bonds break.
When a salt like NaCl dissolves in water, the NaCl breaks in to ions Na+ and Cl-.
The water molecules now surround these ions.
The slightly negative oxygen end of water molecule gets near the Na+, while the slightly positive Hydrogen of water molecule gets near the Cl-.
So before salt sample dissolve, the water molecules were highly ordered due to hydrogen bonding. Now after salt dissolve there is a decrease in order and thus an increase in disorder of the water molecules.
Due to increase in disorder, entropy which is a measure of disorder increases. Since entropy increases, delta S for the process is positive.
