Correct option is (a) Due to addition of solute
Best explanation: Boiling point elevation is the temperature change of the boiling point of a solvent caused by adding a solute. If the vapor pressure is lowered, the relative number of particles becoming a gas is decreased. In order to reach equilibrium between vapor pressure and atmospheric pressure, more energy is added to force the particles at the surface of the liquid to release to the gaseous state. This increase results in the liquid boiling at a higher temperature.