Describe how to correctly prepare 400 mL of 0.6 M NaOH starting from solid NaOH.

Answer 1

You want how many moles? That's mols = M x L = 0.6 x 0.400 L = ?
How many grams is that? That's mols = grams/molar mass. You know molar mass and mols solve for grams NaOH.
Take that many grams of PURE solid NaOH, add the solid pellets to a 400 mL volumetric flask, add some water, swirl to dissolve, let cool, add distilled water to the mark on the flask, stopper, mix thoroughly, label.
NOTE: NaOH is not a primary standard as it comes out of the reagent bottle.It absorbs CO2 from the air and it's quick to do so. This is an OK answer if a freshman class but it isn't a good way for accurate work. If this is in advanced chemistry this is not an OK answer UNLESS you have PURE NaOH.