Osmotic pressure of a solution is 12 atm. What is the concentration of NaCl solution which is isotonic to the given solution at 300 K? $R = 0.082 \text{ L atm K}^{-1} \text{ mol}^{-1}$. Assume 100\% dissociation.
(A) 0.4878 M
(B) 0.02439 M
(C) 0.2439 M
(D) 0.04878 M