[Radu]

    There are two solutions, containing (NPCl₂)_n and (NPCl₂)_n+1. Determine n, considering that the weight percentages of the substances in the two solutions are equal and that the differences between crystallization temperatures of this solutions relate as Δt₁:Δt₂=0.75:1.
      I don't understand why they use the formula Δt=(k*ω*1000)/(100-ω)*μ . It appears to me that the formula is derived from   the dropping of the freezing point, but the constant includes Δ_fusionH, which is not the same for the two substances.
     They simply divide and obtain  Δt₁:Δt₂=μ₂/μ₁. then where does this formula come from?(ω-weight percentage, it is specified.
     

[Borek]

Cryoscopic constant is a function of enthalpy of fusion of the pure solvent, not of the solute.

[Radu]

Surely, thanks!