A solution made by dissolving 40 g NaOH in 1000 g of H_2 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.