What is the osmolarity of a solution that contains 7.6g NaCl in 420 mL of solution?

Answer 1

For electrolytes

π = iCRT where i is the Vant Hoff coefficient.
For NaCl assume i=2 (though experimentally it should be a bit lower and also a function of temperature and concentration)
C=mole/V and mole=mass/MW. Thus

π= i*mass*R*T / (V*MW)

You don't define the temperature. I assume it is 25 Celsius thus T=298 Kelvin

π =2*7.6* 0.082*298 / (0.42*58.5)
=15.1 atm