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

Answer: Option A

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)
$$\begin{array}{rl}& =\frac{0.5\times 250}{1000}\\ & =\frac{125}{1000}\\ & =0.125\text{ mol}\end{array}$$
Molar mass of NaOH = 40g
Mass of NaOH required in grams
$$\begin{array}{rl}& =0.125\times 40\\ & =5\text{g}\end{array}$$