Answer
0.500 M
Work Step by Step
Recall: Molarity = Number of moles of solute÷ Volume of solution in litre.
Moles of NaOH= $\frac{8.0g}{39.997g/mol}$= 0.200 mol
Volume of solution in litre= 400 mL×$\frac{1L}{1000mL}$= 0.400 L
Then, Molarity= $\frac{0.200mol}{0.400L}$= 0.500 mol/L = 0.500 M NaOH solution.
