A100-cm3 container has 4 g of ideal gas in it at 250 kpa. if the volume is changed to 50 cm3 and the temperature remains constant, what is its new density? 80 kg/m3 250 kg/m3 400 kg/m3 50 kg/m3

Since you're giving us the original and final volumes, as well as the mass, and all you want to know is density, we don't actually care about temperature or pressure.  Let um do whatever they want to do.

The new mass is the same as the original mass ... 4 grams.

The new volume is 50 cm³.

The new density is (mass)/(volume) = (4g) / (50 cm³) = 0.08 g/cm³