Ebullioscopy is concerned with: A. osmotic pressure of a solution B. elevation of boiling point of a solution C. depression in freezing point of a solution D. relative lowering in vapour pressure of a solution

Ebullioscopy is the study of the elevation of the boiling point of a solution compared to that of the pure solvent. Therefore, the correct answer is:

B. elevation of boiling point of a solution

Explanation:
Ebullioscopy derives from the term "ebullio," which means to boil. It specifically relates to how the presence of a solute in a solvent alters the boiling point of that solvent.

When a non-volatile solute is dissolved in a solvent, it causes the boiling point of the solvent to increase. This phenomenon is due to the solute particles interfering with the ability of the solvent molecules to escape into the vapor phase, thus requiring more heat (higher temperature) to reach the boiling point.

The other options are related to different colligative properties of solutions:

A. osmotic pressure of a solution refers to the pressure required to prevent the flow of solvent into a solution through a semipermeable membrane.
C. depression in freezing point of a solution is the decrease in the freezing point of a solvent when a solute is added, which is known as freezing point depression.
D. relative lowering in vapor pressure of a solution refers to the decrease in vapor pressure that occurs when a solute is added to a solvent.
In summary, ebullioscopy focuses on the elevation of the boiling point, making option B the correct choice.