To prepare 250 mL 0.5N NaOH solution, NaOH needed is

To prepare 250 mL 0.5N NaOH solution,
$${\text{No}}{\text{.}}\,{\text{of}}\,{\text{moles}}\left( {\text{n}} \right) = \frac{{{\text{Molarity}} \times {\text{V}}\left( {{\text{ml}}} \right)}}{{1000}}$$
Given, volume of the solution = 250 ml
M = 0.5 M
Therefore, No.of moles (n)
$$\eqalign{ & = \frac{{0.5 \times 250}}{{1000}} \cr & = \frac{{125}}{{1000}} \cr & = 0.125{\text{ mol}} \cr} $$
Molar mass of NaOH = 40g
Mass of NaOH required in grams
$$\eqalign{ & = 0.125 \times 40 \cr & = 5\,{\text{g}} \cr} $$