Answer: D = 239.2g/92cm^3 = 2.6g/cm^3
Explanation: Density is defined as the amount of mass in a given volume, where the equation for the density is:

in this case, the mass is m=239.2g and the volume is 92cm^3
then the density is:
D = 239.2g/92cm^3 = 2.6g/cm^3
This means that each square centimeter of obsidian weights 2.6g