Answer
See the answer below.
Work Step by Step
For ionic compounds, assuming complete dissociation, the effect on colligative properties is proportional to molality of the ions, i.e, the $i.m$ factor:
a) KBr $2\times 0.20\ m=0.40\ m$, sugar (nonionic) 0.30 m; the KBr solution will have a higher boiling point because of the bigger boiling point elevation.
b) NH4NO3 $2\times 0.12\ m=0.24\ m$, Na2CO3 $3\times 0.10\ m=0.30\ m$; the solution with Na2CO3 will have the lower freezing point because of the bigger freezing point depression.
