Answer
See the answer below.
Work Step by Step
a) Molality:
$\Delta T_f=K_fm\rightarrow -0.542^{\circ}C=-5.12^{\circ}C/m\times m$
$m=0.106\ m$
Number of moles of the dimer:
$0.106\ m\times (10/1000)kg=0.00106\ mol$
Molar mass:
$0.503\ g\div 0.00106\ mol=475.2\ g/mol$
b) A portion of the dimer dissociates into two monomers, which causes the molar mass calculated to be lower than the actual.
