Question

how much NaOH should be dissolved in 2L water to prepare M/10 solution?

Answer 1

1.5 litres
....................

Answer 2

Molarity= (Wt. of NaOH/M.Wt.)x(1000/Volume of the solution)

2M=(Wt. of NaOH/40)x(1000/250)

Wt. of NaOH=(2x40)x(250/1000)=80/4=20 g

Wt. of NaOH=20 g

20 g of NaOH should be added to water (in a 250 ml volumetric flask) to prepare 250 ml of 2M NaOH solution.