Answer
See the answer below.
Work Step by Step
Boiling point elevation and vapor pressure depression are proportional to $i.m$ and assuming total ionic dissociation, i is the number of ions per compound.
a) sugar 0.15m, Na2SO4: $3\times 0.10\ m=0.30\ m$ -> the Na2SO4 will have a higher boiling point
b) NH4NO3 $2\times 0.30\ m=0.60\ m$, Na2SO4 $3\times 0.15\ m=0.45\ m$ -> NH4NO3 will have a higher vapor pressure (Na2SO4 will have a higher vapor pressure depression).
