a,because water evaporates and salt settles down and this is the method used to get salt from sea water

Understanding Saturated Solutions
A saturated solution is a solution in which the maximum amount of solute (in this case, NaCl) has been dissolved at a given temperature. When the solution is heated, the solubility of NaCl increases, allowing more solute to dissolve.

Effect of Heating on NaCl Saturated Solution
When a saturated solution of NaCl is heated, it can lead to the following scenarios:

1. Becoming Supersaturated
- Upon heating, if the solution is allowed to cool without any disturbance, it can become supersaturated.
- In a supersaturated solution, the concentration of solute exceeds the solubility limit at that temperature. This state is unstable and can lead to crystallization when disturbed.

2. Becoming Unsaturated
- If more NaCl is added to the heated solution, it may dissolve until it reaches the new saturation point at the elevated temperature.
- Once the solution cools, it will still remain unsaturated if the solute concentration is below the saturation point for that lower temperature.

3. Remaining Saturated
- If the solution is saturated at a higher temperature, it remains saturated as long as the cooling process occurs without any solute being added or crystallization initiated.

Conclusion
The answer to the question is that a saturated solution of NaCl on heating can become **supersaturated** if cooled without disturbance, or it may remain **saturated** if the solute concentration stays consistent with the temperature. The exact outcome depends on the conditions during the cooling phase.