The correct answer to this question is D, 8.56m. Also known as molal concentration, molality is a measurement, which measures a solute's concentration. It is measured in terms of the amount of the substance in the mass of the solvent. mol/kg is the unit for molality.
The earliest recorded discovery of this measurement is by chemists G.N. Lewis and M. Randall, through their 1923 publication Thermodynamics and the Free Energies of Chemical Substances. Molality can be measured by mulitplying the number of grams by 1 kilogram over 1,000 grams. This question would normally be found on science tests, specifically in a chemistry course.