The addition of a non-volatile solute to a solvent can cause several changes in the properties of the resulting solution. One of the most significant changes is the reduction in the equilibrium vapor pressure of the solution.

A) Reduction in equilibrium vapor pressure of the solution:
When a non-volatile solute is added to a solvent, the solute particles mix with the solvent particles to form a solution. The solute particles occupy space between the solvent particles, which reduces the number of solvent particles available at the surface of the solution. As a result, fewer solvent particles can escape into the vapor phase, leading to a decrease in the equilibrium vapor pressure of the solution compared to that of the pure solvent.

This reduction in vapor pressure can be explained using Raoult's law, which states that the vapor pressure of a solution is directly proportional to the mole fraction of the solvent in the solution. The presence of the non-volatile solute reduces the mole fraction of the solvent, resulting in a lower vapor pressure.

B) Increase in melting point of the solution:
The addition of a non-volatile solute also increases the melting point of the solution compared to that of the pure solvent. This can be explained by the phenomenon of freezing point depression. The solute particles disrupt the regular arrangement of the solvent particles, making it more difficult for the solvent to solidify. As a result, a lower temperature is required to freeze the solution, leading to an increase in the melting point.

C) Decrease in the boiling point of the solution:
In contrast to the melting point, the addition of a non-volatile solute increases the boiling point of the solution compared to that of the pure solvent. This can be explained by the phenomenon of boiling point elevation. The solute particles lower the vapor pressure of the solution, meaning that a higher temperature is required to reach the same vapor pressure as the pure solvent. As a result, the boiling point of the solution is higher.

D) Osmosis of solute in the solution:
Osmosis refers to the movement of solvent molecules from an area of lower solute concentration to an area of higher solute concentration through a semi-permeable membrane. This process is not specifically caused by the addition of a non-volatile solute to a solvent, but rather by the presence of a concentration gradient across a semi-permeable membrane.