A solution made by dissolving 40 g NaOH in 1000 g of $\mathrm{H}_2 \mathrm{O}$ is

Number of moles of $\mathrm{NaOH}(n)$ $=\frac{\text { weight in } \mathrm{g}}{\text { molar mass }}$ $=\frac{40}{40}=1$ As molality of a solution is defined as the number of moles of the solute dissolved in $1000 \mathrm{~g}(1 \mathrm{~kg})$ of the solvent, thus the given solution of NaOH is ' 1 molal' solution.