The unit of ebullioscopic constant is

Ebullioscopic constant or Molal elevation constant is the elevation in the boiling point produced when one mole of the solute is dissolved in one kilogram of solvent.

$\because {\mathrm{K}}_{\mathrm{b}}=\frac{∆{\mathrm{T}}_b}{\mathrm{m}}$
 The unit of ebullioscopic constant (K) is $\mathrm{K} \mathrm{kg} {\mathrm{mol}}^{-1}\text{ or }\mathrm{K}{\text{ (molality) }}^{-1}$