The unit of Ebullioscopic constant is:

1. K kg mol-1 or K (molality)-1

2. mol kg K-1 or K-1 (molality)

3. kg mol-1 K-1 or K-1 (molality)-1

4. K mol kg-1 or K (molality)

Hint: Ebullioscopic constant is same as molal elevation constant
 As we know from elevation in boiling point that
ΔTb=Kbm
Kb=ΔTbm
Unit of Kb unit of ΔTb unit of m=K molality 
=Kmol kg-1 = K mol-1 kg