Answer: A, B, C
Solving Cα2+Kaα−Ka=0 gives α=0.0347 at 0.0800 and α=0.0683 at 0.0200 (dilution favours dissociation). Then i=1.0347 and 1.0683, so ΔTf/(Kfm)=i is nearer 1 for the more concentrated solution. ΔTf values are 0.1540 K and 0.0397 K; the ratio is 3.874, not 4, because i differs.