Answer:
2M of NaCl has lower vapour pressure and required more energy to reach its boiling point.
Explanations:
What is vapor pressure?
This is the pressure exerted on the surface of a liquid. The higher the pressure, the higher the boiling point.
The concentration of any solute has effect on their vapor pressure and their boiling point. The higher the concentration of a solute, the lower their vapour pressure gets and this is normally due to the fewer solvent molecules present at the top of the solution.
Since the vapor pressure is reduced due to high concentration, hence there will be need for extra energy for the solute (NaCl) to reach its poiling point.
Based on the explanations we can conclude that the boiling point of 2 M NaCI solution higher than the boiling point of 1 M of NaCI solution becaause 2M of NaCl has lower vapour pressure and required more energy to reach its boiling point.