Respuesta :

Willchemistry
Molar mass NH4Cl = 53.491 g/mol

number of moles solute :

n = m / mm

n = 20 / 53.491

n = 0.373 moles

solvent in kg :

13.9 / 1000 => 0.0139 kg 

Therefore:

m = moles / volume

m = 0.373/ 0.0139

=> 26.83 molal