\( 20\% \) of acetic acid is dissociated when its \( 5 \, \mathrm{g} \) is added to \( 500 \, \mathrm{mL} \) of water. The depression in freezing point of such water is ______ \( \times 10^{-3} \, ^\circ\mathrm{C} \).
Atomic mass of \( \mathrm{C} \), \( \mathrm{H} \) and \( \mathrm{O} \) are \( 12 \), \( 1 \) and \( 16 \) a.m.u. respectively.
\([\text{Given: Molal depression constant and density of water are } 1.86 \, \mathrm{K\, mol^{-1}} \text{ and } 1 \, \mathrm{g\, cm^{-3}} \text{ respectively].}\)
