The unit of Boiling point Elevation Constant ( K_b ) is

The correct answer is Option (1) → \(K\, kg\, mol^{-1}\)

The elevation of boiling point of a dilute solution is directly proportional to the molality of the solute, and the constant of proportionality is K_b:

    \( \displaystyle \Delta T_b = K_b\,m \)

The unit of K_b follows by rearranging. \( \Delta T_b \) is in kelvin and molality is in mol kg⁻¹:

    \( \displaystyle K_b = \frac{\Delta T_b}{m} = \frac{\mathrm{K}}{\mathrm{mol\,kg^{-1}}} = \mathrm{K\,kg\,mol^{-1}} \)

Shortcut: Molality has mol in the numerator and kg in the denominator; dividing by it puts kg up and mol down, which only Option (1) has.

NCERT (2026-27 edition):
Elevation of Boiling Point – …