$\begin{aligned} & \text {} \mathrm{m}_2=18 \mathrm{~g}, \mathrm{M}_2=180 \mathrm{~g} \mathrm{~mol}^{-1}, \mathrm{~m}_1=18 \mathrm{~g}, \mathrm{M}_1=18 \mathrm{~g} \\ & \begin{aligned} \Rightarrow \mathrm{n}_2=\frac{\mathrm{m}_2}{\mathrm{M}_2} & =\frac{18}{180}=0.1 \mathrm{~mol} \\ \mathrm{M}_1=18.0 \mathrm{~g} & =18.0 \times 10^{-3} \mathrm{~kg} \\ \Rightarrow \text { molality } & =\frac{\text { Number of moles of solute }}{\text { Mass of solvent in } \mathrm{kg}}=\frac{0.1}{18.0 \times 10^{-3}} \\ & =5.55 \mathrm{~mol} \mathrm{~kg}^{-1} .\end{aligned}\end{aligned}$