Given in the problem is the mass of the liquid (500 grams) and the volume of the liquid (1000 ml = 1000 cm^3).
We can use these two givens to calculate the density of the liquid using the following rule:
density = mass / volume
density = 500 / 1000 = 0.5 grams / cm^3
Comparing the calculated density with the choices we have, we can deduce that the liquid is most likely to be propane with density 0.494 g / cm^3