Question

how can i prepare a saturated solution of sodium chloride in water at 25 degree celcius? what will happen if this solution is cooled at 10 degree celcius ?

Answer 1

A saturated solution is a solution in which no more solute can be dissolve at given temperature. The addition of any more solute will result in the accumulation of that solute in the bottom of the container.
To prepare the saturated solution of NaCl at 25°C, take a measured volume of water (say 100 ml.) in beaker and warm it up to 25°C​. Then add NaCl pinch by pinch at constant stirring and observe the point when no more NaCl is dissolving in water. At that point the added pinch of NaCl will appear at the bottom of beaker and your saturated solution is prepared.
On cooling, crystals(particles) of NaCl separate from the solution. This is a separation technique is known as crystallisation.