How to prepare 250 ml of 0.5M sodium chloride by dissolving solid salt NaCL?

Answer 1

You want how many mols? That's M x L = 0.5 x 0.250 = ?
Then grams NaCl = mols NaCl x molar mass NaCl.

The proper way to proceed is to weigh out the grams NaCl calculated above, transfer the solid quantitatively to a 250 mL volumetric flask, add some distilled or deionized water, swirl until the solid is dissolved, add water to the mark on the volumetric flask, stopper, mix thoroughly, label.