Step 1: Use the formula for depression in freezing point.
Depression in freezing point is given by
\[
\Delta T_f=K_f\times m
\]
where
\[
K_f=\text{molal depression constant}
\]
and
\[
m=\text{molality of solution}
\]
Step 2: Calculate the molality of the solution.
Given:
\[
\text{Moles of solute}=0.05
\]
Mass of water:
\[
500\,g=0.5\,kg
\]
Molality is
\[
m=\frac{\text{moles of solute}}{\text{mass of solvent in kg}}
\]
\[
m=\frac{0.05}{0.5}
\]
\[
m=0.1\,mol\,kg^{-1}
\]
Step 3: Calculate depression in freezing point.
Given,
\[
K_f=1.86\,K\,kg\,mol^{-1}
\]
Therefore,
\[
\Delta T_f=1.86\times 0.1
\]
\[
\Delta T_f=0.186\,K
\]
Step 4: Final conclusion.
Hence, the depression in freezing point is
\[
\boxed{0.186\,K}
\]