Answer
$-5.0^{\circ}C$
Work Step by Step
In 1 kg of the solution:
Mass of solute: $11\%\times1000\ g=110\ g$
Number of moles of solute: $110\ g\div46.07\ g/mol=2.39\ mol$
Molality: $2.39\ mol\div(0.89\ kg)=2.68\ m$
Freezing point depression: $\Delta T_f=K_fm=-1.86^{\circ}C/m\times2.86\ m=-4.99^{\circ}C$
Freezing point: $-5.0^{\circ}C$
