1 mole of NaCl has (23+35.5)g= 58.5g
Therefore, to make 1M/L of solution you will need 58.5g Then to make 0.5M/L you will need 58.5/2=29.25g
If to make 1liter of 0.5M one will need 29.25 grams of NaCl, then250g of NaCl will make
(250g×1L)/29.25g= 8.547liters