How many grams of naoh are needed to prepare 500 ml of 0.125 m naoh?

First let us calculate for the number of moles needed:

moles NaOH = 0.125 M * 0.500 L = 0.0625 mol

The molar mass of NaOH is 40 g/mol, hence the mass is:

mass NaOH = 0.0625 mol * 40 g/mol

mass NaOH = 2.5 grams