The molal elevation constant is the ratio of the elevation in boiling point to

Due to the solute present in the solution, the solution's boiling point is greater than the pure solvent's boiling point. This is called elevation in boiling point and it can be represented as

${\mathrm{\Delta T}}_{\mathrm{b}}={\mathrm{K}}_{\mathrm{b}}\times \text{ molality }$

${\mathrm{K}}_{\mathrm{b}}=\frac{{\mathrm{\Delta T}}_{\mathrm{b}}}{\text{ molality }}$

Therefore Option B is the correct answer