For osmotic pressure, using the van 't Hoff equation: π=iMRT.
The living cell has osmotic pressure of 12 atm.
For an isotonic NaCl solution, the osmotic pressures must be equal.
For NaCl solution: π=i×M×R×T, where i=2 (complete dissociation into Na⁺ and Cl⁻).
12=2×M×0.08×300
12=48M
M=0.25 mol/L
Molar mass of NaCl = 23 + 35.5 = 58.5 g/mol.
Concentration in g/L = 0.25×58.5=14.625≈15 g/L