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

Hint: Ebullioscopy is a chemical technique which is used in finding molecular weights of substances by measuring the extent to which the compounds change its boiling point of a solvent.

Complete step by step solution:
An Ebullioscope is an instrument which is used for measuring the boiling point of a liquid. Additionally, this can be used also for determining the alcoholic strength in a mixture, or for determining the molecular weight of a non-volatile solute. As we know that the boiling point of a liquid at a given external pressure is the temperature at which the vapour pressure of the liquid turns equal to the external pressure. And the whole procedure is based on the principle of boiling-point elevation. The whole process is called ebullioscopy.
Hence, the correct answer is Option B.
The first ebullioscope was invented in 1838 by Honore Brossard-Vidal, and its initial purpose was for measuring the alcoholic content. The advantage of this method was that the boiling point is relatively insensitive to other components such as sugars. Older alcoholic-meters were based on measuring the density, which is more sensitive to the presence of other solutes. Then later came a version which was built by a French chemist, but it had some drawbacks as it was difficult to determine the exact temperature and it was solved by the invention of the Beckmann thermometer. This invention eventually made the ebullioscope a standard instrument for determining the molecular weight of substances in solution with the help of a constant known as the ebullioscopic constant for a solvent.

Note: The sugars and the salts are examples of non-volatile solutes and these are the type of compounds which do not evaporate easily into gas molecules under a given conditions. Non-volatile substances exhibit a low vapour pressure and a high boiling point.