Which procedure is most appropriate, Nacl Molar mass = 58.4 g per mole
250 mL x 0.10 mol/L x 1 L/1000 mL=0.025 mol
0.025 mol NaCl x 58.4 g/mol=1.46 g NaCl
So add 1.46 g NaCl to a certain amount of water less than 250 mL then dilute to 250 mL. If you’re wondering why b is technically incorrect, I’ll explain. If you add 1.46 grams of NaCl to 250 mL of water the volume of the resulting solution would be slightly more than 250 mL which would make the concentration slightly less than 0.10 M.