The correct option is D Al2(SO4)3
Depression in freezing point is given by,
ΔTf=i×Kf×m
where,
ΔTf is the depression in freezing point.
Kf is molal depression constant.
m is molality of solution.
i is van't Hoff factor
Molality of all given solutions are same,
hence,
Depression in freeziong point ∝i
K2SO4→2K+(aq)+SO2−4(aq)
i=3
KCl→K++Cl−
i=2
Al2(SO4)3→2Al3++3SO2−4
i=5
i for C6H12O6 is 1
Hence, option (c) is correct.