posted by Annmarie .
what is the concentration of the chloride ion when enough water is added to 12 grams of sodium chloride to make 4.0 Liters if solution?
(a) 0.025 M (b)0.05 M
(c) 0.1 M (d)0.2
12 g of NaCl is 12/58.5 = 0.205 moles
That gets dissolved into 4.0 l of H2O, resulting Na+ and Cl- concentrations of 0.051 moles/liter. The 0.05M answer is closest to that. They should not have dropped a significant figure.