Given, mass of non-volatile solid =xg Molar mass =78gmol−1 Mass of water =0.5‌kg Kf( water )=1.86Kkg−1mol−1 Lowering in freezing point, ∆Tf=1∘C Using the equation; ∆Tf=Kfm⇒m=‌
∆Tf
Kf
Now, substituting the given values in above formula, m=‌
1
1.86
‌kg We know that molality =‌
‌ Number of moles of solute ‌
‌ Mass of solvent (in ‌kg‌ ) ‌
‌‌
n
M
=‌
1
1.86
[n = number of moles of solute M = mass of solvent in kg ] ‌ So, ‌n=‌